Add i18n support with English and Spanish translations

- Created i18n package with translator and middleware
- Added translation files for English (en.json) and Spanish (es.json)
- Updated all HTTP handlers to use i18n for error/success messages
- Added comprehensive test coverage for i18n (87%)
- Updated CI workflow to use Go 1.24
- All tests passing with 50.8% total coverage

.github/workflows/docker-publish.yml

@@ -17,7 +17,7 @@ jobs:
     - name: Set up Go
       uses: actions/setup-go@v5
       with:
-        go-version: '1.21'
+        go-version: '1.24'
 
     - name: Run tests
       run: go test ./... -v -race -coverprofile=coverage.txt -covermode=atomic
@@ -40,7 +40,7 @@ jobs:
     - name: Set up Go
       uses: actions/setup-go@v5
       with:
-        go-version: '1.21'
+        go-version: '1.24'
 
     - name: Run go vet
       run: go vet ./...
@@ -69,7 +69,7 @@ jobs:
     - name: Set up Go
       uses: actions/setup-go@v5
       with:
-        go-version: '1.21'
+        go-version: '1.24'
 
     - name: Run GoReleaser
       uses: goreleaser/goreleaser-action@v6

cmd/api/main.go

@@ -10,6 +10,7 @@ import (
 
 	"apocapoc-api/internal/application/commands"
 	"apocapoc-api/internal/application/queries"
+	"apocapoc-api/internal/i18n"
 	"apocapoc-api/internal/infrastructure/auth"
 	"apocapoc-api/internal/infrastructure/config"
 	"apocapoc-api/internal/infrastructure/crypto"
@@ -86,6 +87,11 @@ func main() {
 	refreshTokenRepo := sqlite.NewRefreshTokenRepository(db.Conn())
 	passwordResetTokenRepo := sqlite.NewPasswordResetTokenRepository(db.Conn())
 
+	translator, err := i18n.NewTranslator()
+	if err != nil {
+		log.Fatalf("Failed to create translator: %v", err)
+	}
+
 	registerHandler := commands.NewRegisterUserHandler(userRepo, passwordHasher, emailService, cfg.AppURL, cfg.RegistrationMode, sendWelcomeEmail)
 	loginHandler := queries.NewLoginUserHandler(userRepo, passwordHasher)
 	refreshTokenHandler := queries.NewRefreshTokenHandler(refreshTokenRepo, userRepo)
@@ -107,13 +113,13 @@ func main() {
 	markHandler := commands.NewMarkHabitHandler(entryRepo, habitRepo)
 	unmarkHandler := commands.NewUnmarkHabitHandler(habitRepo, entryRepo)
 
-	authHandlers := httpInfra.NewAuthHandlers(registerHandler, loginHandler, refreshTokenHandler, revokeTokenHandler, revokeAllTokensHandler, verifyEmailHandler, resendVerificationEmailHandler, requestPasswordResetHandler, resetPasswordHandler, jwtService, refreshTokenRepo, refreshTokenExpiry)
+	authHandlers := httpInfra.NewAuthHandlers(registerHandler, loginHandler, refreshTokenHandler, revokeTokenHandler, revokeAllTokensHandler, verifyEmailHandler, resendVerificationEmailHandler, requestPasswordResetHandler, resetPasswordHandler, jwtService, refreshTokenRepo, refreshTokenExpiry, translator)
-	habitHandlers := httpInfra.NewHabitHandlers(createHandler, getTodaysHandler, getUserHabitsHandler, getHabitByIDHandler, getHabitEntriesHandler, updateHandler, archiveHandler, markHandler, unmarkHandler, userRepo)
+	habitHandlers := httpInfra.NewHabitHandlers(createHandler, getTodaysHandler, getUserHabitsHandler, getHabitByIDHandler, getHabitEntriesHandler, updateHandler, archiveHandler, markHandler, unmarkHandler, userRepo, translator)
-	statsHandlers := httpInfra.NewStatsHandlers(getHabitStatsHandler)
+	statsHandlers := httpInfra.NewStatsHandlers(getHabitStatsHandler, translator)
 	healthHandlers := httpInfra.NewHealthHandlers(db.Conn())
-	userHandlers := httpInfra.NewUserHandlers(deleteUserHandler)
+	userHandlers := httpInfra.NewUserHandlers(deleteUserHandler, translator)
 
-	router := httpInfra.NewRouter(cfg.AppURL, habitHandlers, authHandlers, statsHandlers, healthHandlers, userHandlers, jwtService)
+	router := httpInfra.NewRouter(cfg.AppURL, habitHandlers, authHandlers, statsHandlers, healthHandlers, userHandlers, jwtService, translator)
 
 	addr := fmt.Sprintf("0.0.0.0:%s", cfg.Port)
 	log.Printf("Server starting on %s", addr)

go.mod

@@ -34,7 +34,8 @@ require (
 	golang.org/x/exp v0.0.0-20250620022241-b7579e27df2b // indirect
 	golang.org/x/net v0.47.0 // indirect
 	golang.org/x/sys v0.38.0 // indirect
-	golang.org/x/tools v0.36.0 // indirect
+	golang.org/x/text v0.31.0 // indirect
+	golang.org/x/tools v0.38.0 // indirect
 	gopkg.in/alexcesaro/quotedprintable.v3 v3.0.0-20150716171945-2caba252f4dc // indirect
 	gopkg.in/mail.v2 v2.3.1 // indirect
 	gopkg.in/yaml.v2 v2.4.0 // indirect

go.sum

@@ -70,11 +70,13 @@ golang.org/x/exp v0.0.0-20250620022241-b7579e27df2b h1:M2rDM6z3Fhozi9O7NWsxAkg/y
 golang.org/x/exp v0.0.0-20250620022241-b7579e27df2b/go.mod h1:3//PLf8L/X+8b4vuAfHzxeRUl04Adcb341+IGKfnqS8=
 golang.org/x/mod v0.27.0 h1:kb+q2PyFnEADO2IEF935ehFUXlWiNjJWtRNgBLSfbxQ=
 golang.org/x/mod v0.27.0/go.mod h1:rWI627Fq0DEoudcK+MBkNkCe0EetEaDSwJJkCcjpazc=
+golang.org/x/mod v0.29.0 h1:HV8lRxZC4l2cr3Zq1LvtOsi/ThTgWnUk/y64QSs8GwA=
 golang.org/x/net v0.0.0-20210805182204-aaa1db679c0d/go.mod h1:9nx3DQGgdP8bBQD5qxJ1jj9UTztislL4KSBs9R2vV5Y=
 golang.org/x/net v0.47.0 h1:Mx+4dIFzqraBXUugkia1OOvlD6LemFo1ALMHjrXDOhY=
 golang.org/x/net v0.47.0/go.mod h1:/jNxtkgq5yWUGYkaZGqo27cfGZ1c5Nen03aYrrKpVRU=
 golang.org/x/sync v0.16.0 h1:ycBJEhp9p4vXvUZNszeOq0kGTPghopOL8q0fq3vstxw=
 golang.org/x/sync v0.16.0/go.mod h1:1dzgHSNfp02xaA81J2MS99Qcpr2w7fw1gpm99rleRqA=
+golang.org/x/sync v0.18.0 h1:kr88TuHDroi+UVf+0hZnirlk8o8T+4MrK6mr60WkH/I=
 golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20210423082822-04245dca01da/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.6.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
@@ -82,9 +84,13 @@ golang.org/x/sys v0.38.0 h1:3yZWxaJjBmCWXqhN1qh02AkOnCQ1poK6oF+a7xWL6Gc=
 golang.org/x/sys v0.38.0/go.mod h1:OgkHotnGiDImocRcuBABYBEXf8A9a87e/uXjp9XT3ks=
 golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
 golang.org/x/text v0.3.6/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
+golang.org/x/text v0.31.0 h1:aC8ghyu4JhP8VojJ2lEHBnochRno1sgL6nEi9WGFGMM=
+golang.org/x/text v0.31.0/go.mod h1:tKRAlv61yKIjGGHX/4tP1LTbc13YSec1pxVEWXzfoeM=
 golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 golang.org/x/tools v0.36.0 h1:kWS0uv/zsvHEle1LbV5LE8QujrxB3wfQyxHfhOk0Qkg=
 golang.org/x/tools v0.36.0/go.mod h1:WBDiHKJK8YgLHlcQPYQzNCkUxUypCaa5ZegCVutKm+s=
+golang.org/x/tools v0.38.0 h1:Hx2Xv8hISq8Lm16jvBZ2VQf+RLmbd7wVUsALibYI/IQ=
+golang.org/x/tools v0.38.0/go.mod h1:yEsQ/d/YK8cjh0L6rZlY8tgtlKiBNTL14pGDJPJpYQs=
 gopkg.in/alexcesaro/quotedprintable.v3 v3.0.0-20150716171945-2caba252f4dc h1:2gGKlE2+asNV9m7xrywl36YYNnBG5ZQ0r/BOOxqPpmk=
 gopkg.in/alexcesaro/quotedprintable.v3 v3.0.0-20150716171945-2caba252f4dc/go.mod h1:m7x9LTH6d71AHyAX77c9yqWCCa3UKHcVEj9y7hAtKDk=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=

internal/i18n/i18n.go

@@ -0,0 +1,122 @@
+package i18n
+
+import (
+	_ "embed"
+	"encoding/json"
+	"fmt"
+	"strings"
+
+	"golang.org/x/text/language"
+)
+
+//go:embed locales/en.json
+var enTranslations []byte
+
+//go:embed locales/es.json
+var esTranslations []byte
+
+type Translations struct {
+	Errors     map[string]string `json:"errors"`
+	Success    map[string]string `json:"success"`
+	Validation map[string]string `json:"validation"`
+	Emails     map[string]string `json:"emails"`
+}
+
+type Translator struct {
+	translations map[language.Tag]Translations
+	matcher      language.Matcher
+}
+
+func NewTranslator() (*Translator, error) {
+	var enTrans, esTrans Translations
+
+	if err := json.Unmarshal(enTranslations, &enTrans); err != nil {
+		return nil, fmt.Errorf("failed to load English translations: %w", err)
+	}
+
+	if err := json.Unmarshal(esTranslations, &esTrans); err != nil {
+		return nil, fmt.Errorf("failed to load Spanish translations: %w", err)
+	}
+
+	translations := map[language.Tag]Translations{
+		language.English: enTrans,
+		language.Spanish: esTrans,
+	}
+
+	matcher := language.NewMatcher([]language.Tag{
+		language.English,
+		language.Spanish,
+	})
+
+	return &Translator{
+		translations: translations,
+		matcher:      matcher,
+	}, nil
+}
+
+func (t *Translator) GetLanguage(acceptLanguage string) language.Tag {
+	if acceptLanguage == "" {
+		return language.English
+	}
+
+	tags, _, err := language.ParseAcceptLanguage(acceptLanguage)
+	if err != nil || len(tags) == 0 {
+		return language.English
+	}
+
+	_, index, _ := t.matcher.Match(tags...)
+	supportedTags := []language.Tag{language.English, language.Spanish}
+	if index < len(supportedTags) {
+		return supportedTags[index]
+	}
+
+	return language.English
+}
+
+func (t *Translator) Translate(lang language.Tag, category, key string) string {
+	trans, ok := t.translations[lang]
+	if !ok {
+		trans = t.translations[language.English]
+	}
+
+	var categoryMap map[string]string
+	switch category {
+	case "errors":
+		categoryMap = trans.Errors
+	case "success":
+		categoryMap = trans.Success
+	case "validation":
+		categoryMap = trans.Validation
+	case "emails":
+		categoryMap = trans.Emails
+	default:
+		return key
+	}
+
+	if value, ok := categoryMap[key]; ok {
+		return value
+	}
+
+	return key
+}
+
+func (t *Translator) Error(lang language.Tag, key string) string {
+	return t.Translate(lang, "errors", key)
+}
+
+func (t *Translator) Success(lang language.Tag, key string) string {
+	return t.Translate(lang, "success", key)
+}
+
+func (t *Translator) Validation(lang language.Tag, key string) string {
+	return t.Translate(lang, "validation", key)
+}
+
+func (t *Translator) Email(lang language.Tag, key string) string {
+	return t.Translate(lang, "emails", key)
+}
+
+func (t *Translator) TranslateValidationError(lang language.Tag, field, validationKey string) string {
+	message := t.Validation(lang, validationKey)
+	return strings.ReplaceAll(message, field, field)
+}

internal/i18n/i18n_test.go

@@ -0,0 +1,252 @@
+package i18n
+
+import (
+	"testing"
+
+	"golang.org/x/text/language"
+)
+
+func TestNewTranslator(t *testing.T) {
+	translator, err := NewTranslator()
+	if err != nil {
+		t.Fatalf("Failed to create translator: %v", err)
+	}
+
+	if translator == nil {
+		t.Fatal("Expected translator to be non-nil")
+	}
+
+	if translator.translations == nil {
+		t.Fatal("Expected translations map to be initialized")
+	}
+
+	if len(translator.translations) != 2 {
+		t.Errorf("Expected 2 languages, got %d", len(translator.translations))
+	}
+}
+
+func TestGetLanguage(t *testing.T) {
+	translator, _ := NewTranslator()
+
+	tests := []struct {
+		name           string
+		acceptLanguage string
+		expected       language.Tag
+	}{
+		{
+			name:           "English",
+			acceptLanguage: "en-US",
+			expected:       language.English,
+		},
+		{
+			name:           "Spanish",
+			acceptLanguage: "es-ES",
+			expected:       language.Spanish,
+		},
+		{
+			name:           "Empty defaults to English",
+			acceptLanguage: "",
+			expected:       language.English,
+		},
+		{
+			name:           "Unknown language defaults to English",
+			acceptLanguage: "fr-FR",
+			expected:       language.English,
+		},
+		{
+			name:           "Spanish with quality",
+			acceptLanguage: "es-ES,es;q=0.9",
+			expected:       language.Spanish,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := translator.GetLanguage(tt.acceptLanguage)
+			if result != tt.expected {
+				t.Errorf("Expected %v, got %v", tt.expected, result)
+			}
+		})
+	}
+}
+
+func TestError(t *testing.T) {
+	translator, _ := NewTranslator()
+
+	tests := []struct {
+		name     string
+		lang     language.Tag
+		key      string
+		expected string
+	}{
+		{
+			name:     "English error message",
+			lang:     language.English,
+			key:      "invalid_request_body",
+			expected: "Invalid request body",
+		},
+		{
+			name:     "Spanish error message",
+			lang:     language.Spanish,
+			key:      "invalid_request_body",
+			expected: "Cuerpo de solicitud inválido",
+		},
+		{
+			name:     "Missing key returns key",
+			lang:     language.English,
+			key:      "non_existent_key",
+			expected: "non_existent_key",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := translator.Error(tt.lang, tt.key)
+			if result != tt.expected {
+				t.Errorf("Expected '%s', got '%s'", tt.expected, result)
+			}
+		})
+	}
+}
+
+func TestSuccess(t *testing.T) {
+	translator, _ := NewTranslator()
+
+	tests := []struct {
+		name     string
+		lang     language.Tag
+		key      string
+		expected string
+	}{
+		{
+			name:     "English success message",
+			lang:     language.English,
+			key:      "logged_out",
+			expected: "Successfully logged out",
+		},
+		{
+			name:     "Spanish success message",
+			lang:     language.Spanish,
+			key:      "logged_out",
+			expected: "Sesión cerrada exitosamente",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := translator.Success(tt.lang, tt.key)
+			if result != tt.expected {
+				t.Errorf("Expected '%s', got '%s'", tt.expected, result)
+			}
+		})
+	}
+}
+
+func TestValidation(t *testing.T) {
+	translator, _ := NewTranslator()
+
+	tests := []struct {
+		name     string
+		lang     language.Tag
+		key      string
+		expected string
+	}{
+		{
+			name:     "English validation message",
+			lang:     language.English,
+			key:      "email_required",
+			expected: "email is required",
+		},
+		{
+			name:     "Spanish validation message",
+			lang:     language.Spanish,
+			key:      "email_required",
+			expected: "el email es requerido",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := translator.Validation(tt.lang, tt.key)
+			if result != tt.expected {
+				t.Errorf("Expected '%s', got '%s'", tt.expected, result)
+			}
+		})
+	}
+}
+
+func TestEmail(t *testing.T) {
+	translator, _ := NewTranslator()
+
+	tests := []struct {
+		name     string
+		lang     language.Tag
+		key      string
+		expected string
+	}{
+		{
+			name:     "English email message",
+			lang:     language.English,
+			key:      "welcome_subject",
+			expected: "Welcome to Apocapoc!",
+		},
+		{
+			name:     "Spanish email message",
+			lang:     language.Spanish,
+			key:      "welcome_subject",
+			expected: "¡Bienvenido a Apocapoc!",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := translator.Email(tt.lang, tt.key)
+			if result != tt.expected {
+				t.Errorf("Expected '%s', got '%s'", tt.expected, result)
+			}
+		})
+	}
+}
+
+func TestTranslate(t *testing.T) {
+	translator, _ := NewTranslator()
+
+	tests := []struct {
+		name     string
+		lang     language.Tag
+		category string
+		key      string
+		expected string
+	}{
+		{
+			name:     "Valid category and key",
+			lang:     language.English,
+			category: "errors",
+			key:      "user_not_found",
+			expected: "User not found",
+		},
+		{
+			name:     "Invalid category returns key",
+			lang:     language.English,
+			category: "invalid_category",
+			key:      "some_key",
+			expected: "some_key",
+		},
+		{
+			name:     "Unsupported language fallback to English",
+			lang:     language.French,
+			category: "errors",
+			key:      "user_not_found",
+			expected: "User not found",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := translator.Translate(tt.lang, tt.category, tt.key)
+			if result != tt.expected {
+				t.Errorf("Expected '%s', got '%s'", tt.expected, result)
+			}
+		})
+	}
+}

internal/i18n/locales/en.json

@@ -0,0 +1,109 @@
+{
+  "errors": {
+    "invalid_request_body": "Invalid request body",
+    "email_already_registered": "Email already registered",
+    "registration_closed": "Registration is currently closed",
+    "failed_register_user": "Failed to register user",
+    "invalid_credentials": "Invalid email or password",
+    "email_not_verified": "Please verify your email before logging in",
+    "failed_login": "Failed to login",
+    "failed_generate_token": "Failed to generate token",
+    "failed_create_refresh_token": "Failed to create refresh token",
+    "failed_save_refresh_token": "Failed to save refresh token",
+    "invalid_expired_refresh_token": "Invalid or expired refresh token",
+    "failed_refresh_token": "Failed to refresh token",
+    "refresh_token_not_found": "Refresh token not found",
+    "invalid_refresh_token": "Invalid refresh token",
+    "user_not_authenticated": "User not authenticated",
+    "failed_get_user": "Failed to get user",
+    "failed_get_habits": "Failed to get habits",
+    "failed_create_habit": "Failed to create habit",
+    "habit_not_found": "Habit not found",
+    "access_denied": "Access denied",
+    "failed_get_habit": "Failed to get habit",
+    "invalid_input": "Invalid input",
+    "failed_update_habit": "Failed to update habit",
+    "failed_archive_habit": "Failed to archive habit",
+    "failed_get_habit_entries": "Failed to get habit entries",
+    "invalid_date_format": "Invalid date format (use YYYY-MM-DD)",
+    "invalid_page_parameter": "Invalid 'page' parameter",
+    "invalid_limit_parameter": "Invalid 'limit' parameter (must be 1-100)",
+    "pagination_required": "Pagination required: provide 'limit' parameter or use date range ≤ 1 year",
+    "invalid_from_date_format": "Invalid 'from' date format (use YYYY-MM-DD)",
+    "invalid_to_date_format": "Invalid 'to' date format (use YYYY-MM-DD)",
+    "habit_already_marked": "Habit already marked for this date",
+    "failed_mark_habit": "Failed to mark habit",
+    "habit_entry_not_found": "Habit entry not found",
+    "failed_unmark_habit": "Failed to unmark habit",
+    "invalid_expired_verification_token": "Invalid or expired verification token",
+    "email_already_verified": "Email already verified",
+    "failed_verify_email": "Failed to verify email",
+    "invalid_email": "Invalid email",
+    "user_not_found": "User not found",
+    "failed_send_verification_email": "Failed to send verification email",
+    "email_not_verified_reset": "Please verify your email before resetting password",
+    "failed_send_reset_email": "Failed to send reset email",
+    "invalid_token_or_password": "Invalid or expired token, or password requirements not met",
+    "failed_reset_password": "Failed to reset password",
+    "failed_delete_user": "Failed to delete user",
+    "failed_get_stats": "Failed to get statistics"
+  },
+  "success": {
+    "registration_with_verification": "Registration successful. Please check your email to verify your account.",
+    "registration_without_verification": "Registration successful. You can now login.",
+    "logged_out": "Successfully logged out",
+    "email_verified": "Email verified successfully",
+    "verification_email_sent": "Verification email sent successfully",
+    "password_reset_email_sent": "Password reset email sent successfully",
+    "password_reset": "Password reset successfully",
+    "user_deleted": "User and all associated data deleted successfully"
+  },
+  "validation": {
+    "email_required": "email is required",
+    "email_invalid_format": "email must be a valid email address",
+    "email_too_long": "email must not exceed 254 characters",
+    "password_required": "password is required",
+    "password_min_length": "password must be at least 8 characters long",
+    "password_max_length": "password must not exceed 128 characters",
+    "password_uppercase": "password must contain at least one uppercase letter",
+    "password_lowercase": "password must contain at least one lowercase letter",
+    "password_digit": "password must contain at least one digit",
+    "password_special_char": "password must contain at least one special character (!@#$%^&*)",
+    "timezone_required": "timezone is required",
+    "timezone_invalid": "timezone is not a valid IANA timezone",
+    "name_required": "name is required",
+    "name_too_long": "name must not exceed 255 characters",
+    "type_invalid": "type must be one of: BOOLEAN, COUNTER, VALUE",
+    "frequency_invalid": "frequency must be one of: DAILY, WEEKLY, MONTHLY",
+    "specific_days_required": "specific_days is required for WEEKLY frequency",
+    "specific_days_invalid": "specific_days must contain values between 0-6 (0=Sunday, 6=Saturday)",
+    "specific_dates_required": "specific_dates is required for MONTHLY frequency",
+    "specific_dates_invalid": "specific_dates must contain values between 1-31",
+    "target_value_required": "target_value is required for VALUE type",
+    "target_value_positive": "target_value must be positive"
+  },
+  "emails": {
+    "verify_email_subject": "Verify your email address",
+    "verify_email_title": "Welcome! Please verify your email",
+    "verify_email_body": "Thank you for registering. Please click the link below to verify your email address:",
+    "verify_email_link": "Verify Email",
+    "verify_email_expiry": "This link will expire in 24 hours.",
+    "verify_email_ignore": "If you didn't create an account, you can safely ignore this email.",
+    "resend_verification_subject": "Verify your email address",
+    "resend_verification_title": "Verify your email address",
+    "resend_verification_body": "Please click the link below to verify your email address:",
+    "resend_verification_link": "Verify Email",
+    "resend_verification_expiry": "This link will expire in 24 hours.",
+    "resend_verification_ignore": "If you didn't request this, you can safely ignore this email.",
+    "password_reset_subject": "Password Reset Request",
+    "password_reset_title": "Password Reset Request",
+    "password_reset_body": "You have requested to reset your password. Please click the link below:",
+    "password_reset_link": "Reset Password",
+    "password_reset_expiry": "This link will expire in 1 hour.",
+    "password_reset_ignore": "If you didn't request this, you can safely ignore this email.",
+    "welcome_subject": "Welcome to Apocapoc!",
+    "welcome_title": "Welcome to Apocapoc!",
+    "welcome_body": "Your email has been verified successfully. You can now start using all features of Apocapoc.",
+    "welcome_enjoy": "Enjoy building better habits!"
+  }
+}

internal/i18n/locales/es.json

@@ -0,0 +1,109 @@
+{
+  "errors": {
+    "invalid_request_body": "Cuerpo de solicitud inválido",
+    "email_already_registered": "El correo electrónico ya está registrado",
+    "registration_closed": "El registro está actualmente cerrado",
+    "failed_register_user": "Error al registrar usuario",
+    "invalid_credentials": "Correo electrónico o contraseña inválidos",
+    "email_not_verified": "Por favor verifica tu correo electrónico antes de iniciar sesión",
+    "failed_login": "Error al iniciar sesión",
+    "failed_generate_token": "Error al generar token",
+    "failed_create_refresh_token": "Error al crear token de actualización",
+    "failed_save_refresh_token": "Error al guardar token de actualización",
+    "invalid_expired_refresh_token": "Token de actualización inválido o expirado",
+    "failed_refresh_token": "Error al actualizar token",
+    "refresh_token_not_found": "Token de actualización no encontrado",
+    "invalid_refresh_token": "Token de actualización inválido",
+    "user_not_authenticated": "Usuario no autenticado",
+    "failed_get_user": "Error al obtener usuario",
+    "failed_get_habits": "Error al obtener hábitos",
+    "failed_create_habit": "Error al crear hábito",
+    "habit_not_found": "Hábito no encontrado",
+    "access_denied": "Acceso denegado",
+    "failed_get_habit": "Error al obtener hábito",
+    "invalid_input": "Entrada inválida",
+    "failed_update_habit": "Error al actualizar hábito",
+    "failed_archive_habit": "Error al archivar hábito",
+    "failed_get_habit_entries": "Error al obtener entradas de hábito",
+    "invalid_date_format": "Formato de fecha inválido (usa AAAA-MM-DD)",
+    "invalid_page_parameter": "Parámetro 'page' inválido",
+    "invalid_limit_parameter": "Parámetro 'limit' inválido (debe ser 1-100)",
+    "pagination_required": "Se requiere paginación: proporciona el parámetro 'limit' o usa un rango de fechas ≤ 1 año",
+    "invalid_from_date_format": "Formato de fecha 'from' inválido (usa AAAA-MM-DD)",
+    "invalid_to_date_format": "Formato de fecha 'to' inválido (usa AAAA-MM-DD)",
+    "habit_already_marked": "El hábito ya está marcado para esta fecha",
+    "failed_mark_habit": "Error al marcar hábito",
+    "habit_entry_not_found": "Entrada de hábito no encontrada",
+    "failed_unmark_habit": "Error al desmarcar hábito",
+    "invalid_expired_verification_token": "Token de verificación inválido o expirado",
+    "email_already_verified": "El correo electrónico ya está verificado",
+    "failed_verify_email": "Error al verificar correo electrónico",
+    "invalid_email": "Correo electrónico inválido",
+    "user_not_found": "Usuario no encontrado",
+    "failed_send_verification_email": "Error al enviar correo de verificación",
+    "email_not_verified_reset": "Por favor verifica tu correo electrónico antes de restablecer la contraseña",
+    "failed_send_reset_email": "Error al enviar correo de restablecimiento",
+    "invalid_token_or_password": "Token inválido o expirado, o no se cumplen los requisitos de contraseña",
+    "failed_reset_password": "Error al restablecer contraseña",
+    "failed_delete_user": "Error al eliminar usuario",
+    "failed_get_stats": "Error al obtener estadísticas"
+  },
+  "success": {
+    "registration_with_verification": "Registro exitoso. Por favor revisa tu correo electrónico para verificar tu cuenta.",
+    "registration_without_verification": "Registro exitoso. Ya puedes iniciar sesión.",
+    "logged_out": "Sesión cerrada exitosamente",
+    "email_verified": "Correo electrónico verificado exitosamente",
+    "verification_email_sent": "Correo de verificación enviado exitosamente",
+    "password_reset_email_sent": "Correo de restablecimiento de contraseña enviado exitosamente",
+    "password_reset": "Contraseña restablecida exitosamente",
+    "user_deleted": "Usuario y todos los datos asociados eliminados exitosamente"
+  },
+  "validation": {
+    "email_required": "el email es requerido",
+    "email_invalid_format": "el email debe ser una dirección de correo válida",
+    "email_too_long": "el email no debe exceder 254 caracteres",
+    "password_required": "la password es requerida",
+    "password_min_length": "la password debe tener al menos 8 caracteres",
+    "password_max_length": "la password no debe exceder 128 caracteres",
+    "password_uppercase": "la password debe contener al menos una letra mayúscula",
+    "password_lowercase": "la password debe contener al menos una letra minúscula",
+    "password_digit": "la password debe contener al menos un dígito",
+    "password_special_char": "la password debe contener al menos un carácter especial (!@#$%^&*)",
+    "timezone_required": "la timezone es requerida",
+    "timezone_invalid": "la timezone no es una zona horaria IANA válida",
+    "name_required": "el name es requerido",
+    "name_too_long": "el name no debe exceder 255 caracteres",
+    "type_invalid": "el type debe ser uno de: BOOLEAN, COUNTER, VALUE",
+    "frequency_invalid": "la frequency debe ser una de: DAILY, WEEKLY, MONTHLY",
+    "specific_days_required": "specific_days es requerido para frecuencia WEEKLY",
+    "specific_days_invalid": "specific_days debe contener valores entre 0-6 (0=Domingo, 6=Sábado)",
+    "specific_dates_required": "specific_dates es requerido para frecuencia MONTHLY",
+    "specific_dates_invalid": "specific_dates debe contener valores entre 1-31",
+    "target_value_required": "target_value es requerido para tipo VALUE",
+    "target_value_positive": "target_value debe ser positivo"
+  },
+  "emails": {
+    "verify_email_subject": "Verifica tu dirección de correo electrónico",
+    "verify_email_title": "¡Bienvenido! Por favor verifica tu correo electrónico",
+    "verify_email_body": "Gracias por registrarte. Por favor haz clic en el enlace a continuación para verificar tu dirección de correo electrónico:",
+    "verify_email_link": "Verificar correo electrónico",
+    "verify_email_expiry": "Este enlace expirará en 24 horas.",
+    "verify_email_ignore": "Si no creaste una cuenta, puedes ignorar este correo de forma segura.",
+    "resend_verification_subject": "Verifica tu dirección de correo electrónico",
+    "resend_verification_title": "Verifica tu dirección de correo electrónico",
+    "resend_verification_body": "Por favor haz clic en el enlace a continuación para verificar tu dirección de correo electrónico:",
+    "resend_verification_link": "Verificar correo electrónico",
+    "resend_verification_expiry": "Este enlace expirará en 24 horas.",
+    "resend_verification_ignore": "Si no solicitaste esto, puedes ignorar este correo de forma segura.",
+    "password_reset_subject": "Solicitud de restablecimiento de contraseña",
+    "password_reset_title": "Solicitud de restablecimiento de contraseña",
+    "password_reset_body": "Has solicitado restablecer tu contraseña. Por favor haz clic en el enlace a continuación:",
+    "password_reset_link": "Restablecer contraseña",
+    "password_reset_expiry": "Este enlace expirará en 1 hora.",
+    "password_reset_ignore": "Si no solicitaste esto, puedes ignorar este correo de forma segura.",
+    "welcome_subject": "¡Bienvenido a Apocapoc!",
+    "welcome_title": "¡Bienvenido a Apocapoc!",
+    "welcome_body": "Tu correo electrónico ha sido verificado exitosamente. Ya puedes comenzar a usar todas las funcionalidades de Apocapoc.",
+    "welcome_enjoy": "¡Disfruta construyendo mejores hábitos!"
+  }
+}

internal/i18n/middleware.go

@@ -0,0 +1,30 @@
+package i18n
+
+import (
+	"context"
+	"net/http"
+
+	"golang.org/x/text/language"
+)
+
+type contextKey string
+
+const languageKey contextKey = "language"
+
+func LanguageMiddleware(translator *Translator) func(http.Handler) http.Handler {
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			acceptLanguage := r.Header.Get("Accept-Language")
+			lang := translator.GetLanguage(acceptLanguage)
+			ctx := context.WithValue(r.Context(), languageKey, lang)
+			next.ServeHTTP(w, r.WithContext(ctx))
+		})
+	}
+}
+
+func GetLanguageFromContext(ctx context.Context) language.Tag {
+	if lang, ok := ctx.Value(languageKey).(language.Tag); ok {
+		return lang
+	}
+	return language.English
+}

internal/i18n/middleware_test.go

@@ -0,0 +1,99 @@
+package i18n
+
+import (
+	"context"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"golang.org/x/text/language"
+)
+
+func TestLanguageMiddleware(t *testing.T) {
+	translator, _ := NewTranslator()
+	middleware := LanguageMiddleware(translator)
+
+	tests := []struct {
+		name           string
+		acceptLanguage string
+		expectedLang   language.Tag
+	}{
+		{
+			name:           "English header",
+			acceptLanguage: "en-US",
+			expectedLang:   language.English,
+		},
+		{
+			name:           "Spanish header",
+			acceptLanguage: "es-ES",
+			expectedLang:   language.Spanish,
+		},
+		{
+			name:           "No header defaults to English",
+			acceptLanguage: "",
+			expectedLang:   language.English,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var capturedLang language.Tag
+			handler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				capturedLang = GetLanguageFromContext(r.Context())
+				w.WriteHeader(http.StatusOK)
+			})
+
+			wrappedHandler := middleware(handler)
+
+			req := httptest.NewRequest("GET", "/test", nil)
+			if tt.acceptLanguage != "" {
+				req.Header.Set("Accept-Language", tt.acceptLanguage)
+			}
+
+			w := httptest.NewRecorder()
+			wrappedHandler.ServeHTTP(w, req)
+
+			if capturedLang != tt.expectedLang {
+				t.Errorf("Expected language %v, got %v", tt.expectedLang, capturedLang)
+			}
+		})
+	}
+}
+
+func TestGetLanguageFromContext(t *testing.T) {
+	tests := []struct {
+		name     string
+		ctx      context.Context
+		expected language.Tag
+	}{
+		{
+			name:     "Context with English",
+			ctx:      context.WithValue(context.Background(), languageKey, language.English),
+			expected: language.English,
+		},
+		{
+			name:     "Context with Spanish",
+			ctx:      context.WithValue(context.Background(), languageKey, language.Spanish),
+			expected: language.Spanish,
+		},
+		{
+			name:     "Context without language defaults to English",
+			ctx:      context.Background(),
+			expected: language.English,
+		},
+		{
+			name:     "Context with wrong value type defaults to English",
+			ctx:      context.WithValue(context.Background(), languageKey, "invalid"),
+			expected: language.English,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := GetLanguageFromContext(tt.ctx)
+			if result != tt.expected {
+				t.Errorf("Expected %v, got %v", tt.expected, result)
+			}
+		})
+	}
+}

internal/infrastructure/http/auth_handlers.go

@@ -9,6 +9,7 @@ import (
 	"apocapoc-api/internal/application/commands"
 	"apocapoc-api/internal/application/queries"
 	"apocapoc-api/internal/domain/repositories"
+	"apocapoc-api/internal/i18n"
 	"apocapoc-api/internal/infrastructure/auth"
 	appErrors "apocapoc-api/internal/shared/errors"
 )
@@ -26,6 +27,7 @@ type AuthHandlers struct {
 	jwtService                     *auth.JWTService
 	refreshTokenRepo               repositories.RefreshTokenRepository
 	refreshTokenExpiry             time.Duration
+	translator                     *i18n.Translator
 }
 
 func NewAuthHandlers(
@@ -41,6 +43,7 @@ func NewAuthHandlers(
 	jwtService *auth.JWTService,
 	refreshTokenRepo repositories.RefreshTokenRepository,
 	refreshTokenExpiry time.Duration,
+	translator *i18n.Translator,
 ) *AuthHandlers {
 	return &AuthHandlers{
 		registerHandler:                registerHandler,
@@ -55,6 +58,7 @@ func NewAuthHandlers(
 		jwtService:                     jwtService,
 		refreshTokenRepo:               refreshTokenRepo,
 		refreshTokenExpiry:             refreshTokenExpiry,
+		translator:                     translator,
 	}
 }
 
@@ -104,7 +108,7 @@ type LogoutRequest struct {
 func (h *AuthHandlers) Register(w http.ResponseWriter, r *http.Request) {
 	var req RegisterRequest
 	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
-		respondError(w, http.StatusBadRequest, "Invalid request body")
+		respondErrorI18n(w, r, h.translator, http.StatusBadRequest, "invalid_request_body")
 		return
 	}
 
@@ -117,26 +121,27 @@ func (h *AuthHandlers) Register(w http.ResponseWriter, r *http.Request) {
 	result, err := h.registerHandler.Handle(r.Context(), cmd)
 	if err != nil {
 		if errors.Is(err, appErrors.ErrInvalidInput) {
-			respondValidationError(w, err)
+			respondValidationErrorI18n(w, r, h.translator, err)
 			return
 		}
 		if err == appErrors.ErrAlreadyExists {
-			respondError(w, http.StatusConflict, "Email already registered")
+			respondErrorI18n(w, r, h.translator, http.StatusConflict, "email_already_registered")
 			return
 		}
 		if err == appErrors.ErrRegistrationClosed {
-			respondError(w, http.StatusForbidden, "Registration is currently closed")
+			respondErrorI18n(w, r, h.translator, http.StatusForbidden, "registration_closed")
 			return
 		}
-		respondError(w, http.StatusInternalServerError, "Failed to register user")
+		respondErrorI18n(w, r, h.translator, http.StatusInternalServerError, "failed_register_user")
 		return
 	}
 
+	lang := i18n.GetLanguageFromContext(r.Context())
 	var message string
 	if result.EmailVerificationRequired {
-		message = "Registration successful. Please check your email to verify your account."
+		message = h.translator.Success(lang, "registration_with_verification")
 	} else {
-		message = "Registration successful. You can now login."
+		message = h.translator.Success(lang, "registration_without_verification")
 	}
 
 	respondJSON(w, http.StatusCreated, RegisterResponse{
@@ -161,7 +166,7 @@ func (h *AuthHandlers) Register(w http.ResponseWriter, r *http.Request) {
 func (h *AuthHandlers) Login(w http.ResponseWriter, r *http.Request) {
 	var req LoginRequest
 	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
-		respondError(w, http.StatusBadRequest, "Invalid request body")
+		respondErrorI18n(w, r, h.translator, http.StatusBadRequest, "invalid_request_body")
 		return
 	}
 
@@ -173,31 +178,31 @@ func (h *AuthHandlers) Login(w http.ResponseWriter, r *http.Request) {
 	result, err := h.loginHandler.Handle(r.Context(), query)
 	if err != nil {
 		if err == appErrors.ErrNotFound || err == appErrors.ErrInvalidInput {
-			respondError(w, http.StatusUnauthorized, "Invalid email or password")
+			respondErrorI18n(w, r, h.translator, http.StatusUnauthorized, "invalid_credentials")
 			return
 		}
 		if err == appErrors.ErrEmailNotVerified {
-			respondError(w, http.StatusForbidden, "Please verify your email before logging in")
+			respondErrorI18n(w, r, h.translator, http.StatusForbidden, "email_not_verified")
 			return
 		}
-		respondError(w, http.StatusInternalServerError, "Failed to login")
+		respondErrorI18n(w, r, h.translator, http.StatusInternalServerError, "failed_login")
 		return
 	}
 
 	token, err := h.jwtService.GenerateToken(result.UserID, result.Email)
 	if err != nil {
-		respondError(w, http.StatusInternalServerError, "Failed to generate token")
+		respondErrorI18n(w, r, h.translator, http.StatusInternalServerError, "failed_generate_token")
 		return
 	}
 
 	refreshToken, err := queries.CreateRefreshToken(result.UserID, h.refreshTokenExpiry)
 	if err != nil {
-		respondError(w, http.StatusInternalServerError, "Failed to create refresh token")
+		respondErrorI18n(w, r, h.translator, http.StatusInternalServerError, "failed_create_refresh_token")
 		return
 	}
 
 	if err := h.refreshTokenRepo.Create(r.Context(), refreshToken); err != nil {
-		respondError(w, http.StatusInternalServerError, "Failed to save refresh token")
+		respondErrorI18n(w, r, h.translator, http.StatusInternalServerError, "failed_save_refresh_token")
 		return
 	}
 
@@ -223,7 +228,7 @@ func (h *AuthHandlers) Login(w http.ResponseWriter, r *http.Request) {
 func (h *AuthHandlers) Refresh(w http.ResponseWriter, r *http.Request) {
 	var req RefreshRequest
 	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
-		respondError(w, http.StatusBadRequest, "Invalid request body")
+		respondErrorI18n(w, r, h.translator, http.StatusBadRequest, "invalid_request_body")
 		return
 	}
 
@@ -234,27 +239,27 @@ func (h *AuthHandlers) Refresh(w http.ResponseWriter, r *http.Request) {
 	result, err := h.refreshTokenHandler.Handle(r.Context(), query)
 	if err != nil {
 		if err == appErrors.ErrNotFound || err == appErrors.ErrInvalidInput {
-			respondError(w, http.StatusUnauthorized, "Invalid or expired refresh token")
+			respondErrorI18n(w, r, h.translator, http.StatusUnauthorized, "invalid_expired_refresh_token")
 			return
 		}
-		respondError(w, http.StatusInternalServerError, "Failed to refresh token")
+		respondErrorI18n(w, r, h.translator, http.StatusInternalServerError, "failed_refresh_token")
 		return
 	}
 
 	token, err := h.jwtService.GenerateToken(result.UserID, result.Email)
 	if err != nil {
-		respondError(w, http.StatusInternalServerError, "Failed to generate token")
+		respondErrorI18n(w, r, h.translator, http.StatusInternalServerError, "failed_generate_token")
 		return
 	}
 
 	newRefreshToken, err := queries.CreateRefreshToken(result.UserID, h.refreshTokenExpiry)
 	if err != nil {
-		respondError(w, http.StatusInternalServerError, "Failed to create refresh token")
+		respondErrorI18n(w, r, h.translator, http.StatusInternalServerError, "failed_create_refresh_token")
 		return
 	}
 
 	if err := h.refreshTokenRepo.Create(r.Context(), newRefreshToken); err != nil {
-		respondError(w, http.StatusInternalServerError, "Failed to save refresh token")
+		respondErrorI18n(w, r, h.translator, http.StatusInternalServerError, "failed_save_refresh_token")
 		return
 	}
 
@@ -283,7 +288,7 @@ func (h *AuthHandlers) Refresh(w http.ResponseWriter, r *http.Request) {
 func (h *AuthHandlers) Logout(w http.ResponseWriter, r *http.Request) {
 	var req LogoutRequest
 	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
-		respondError(w, http.StatusBadRequest, "Invalid request body")
+		respondErrorI18n(w, r, h.translator, http.StatusBadRequest, "invalid_request_body")
 		return
 	}
 
@@ -294,19 +299,20 @@ func (h *AuthHandlers) Logout(w http.ResponseWriter, r *http.Request) {
 	err := h.revokeTokenHandler.Handle(r.Context(), cmd)
 	if err != nil {
 		if err == appErrors.ErrNotFound {
-			respondError(w, http.StatusNotFound, "Refresh token not found")
+			respondErrorI18n(w, r, h.translator, http.StatusNotFound, "refresh_token_not_found")
 			return
 		}
 		if err == appErrors.ErrInvalidInput {
-			respondError(w, http.StatusBadRequest, "Invalid refresh token")
+			respondErrorI18n(w, r, h.translator, http.StatusBadRequest, "invalid_refresh_token")
 			return
 		}
-		respondError(w, http.StatusInternalServerError, "Failed to revoke token")
+		respondErrorI18n(w, r, h.translator, http.StatusInternalServerError, "failed_refresh_token")
 		return
 	}
 
+	lang := i18n.GetLanguageFromContext(r.Context())
 	respondJSON(w, http.StatusOK, map[string]string{
-		"message": "Successfully logged out",
+		"message": h.translator.Success(lang, "logged_out"),
 	})
 }
 
@@ -333,7 +339,7 @@ type ResendVerificationRequest struct {
 func (h *AuthHandlers) VerifyEmail(w http.ResponseWriter, r *http.Request) {
 	var req VerifyEmailRequest
 	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
-		respondError(w, http.StatusBadRequest, "Invalid request body")
+		respondErrorI18n(w, r, h.translator, http.StatusBadRequest, "invalid_request_body")
 		return
 	}
 
@@ -344,19 +350,20 @@ func (h *AuthHandlers) VerifyEmail(w http.ResponseWriter, r *http.Request) {
 	err := h.verifyEmailHandler.Handle(r.Context(), cmd)
 	if err != nil {
 		if err == appErrors.ErrInvalidInput {
-			respondError(w, http.StatusBadRequest, "Invalid or expired verification token")
+			respondErrorI18n(w, r, h.translator, http.StatusBadRequest, "invalid_expired_verification_token")
 			return
 		}
 		if err == appErrors.ErrAlreadyExists {
-			respondError(w, http.StatusConflict, "Email already verified")
+			respondErrorI18n(w, r, h.translator, http.StatusConflict, "email_already_verified")
 			return
 		}
-		respondError(w, http.StatusInternalServerError, "Failed to verify email")
+		respondErrorI18n(w, r, h.translator, http.StatusInternalServerError, "failed_verify_email")
 		return
 	}
 
+	lang := i18n.GetLanguageFromContext(r.Context())
 	respondJSON(w, http.StatusOK, map[string]string{
-		"message": "Email verified successfully",
+		"message": h.translator.Success(lang, "email_verified"),
 	})
 }
 
@@ -376,7 +383,7 @@ func (h *AuthHandlers) VerifyEmail(w http.ResponseWriter, r *http.Request) {
 func (h *AuthHandlers) ResendVerification(w http.ResponseWriter, r *http.Request) {
 	var req ResendVerificationRequest
 	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
-		respondError(w, http.StatusBadRequest, "Invalid request body")
+		respondErrorI18n(w, r, h.translator, http.StatusBadRequest, "invalid_request_body")
 		return
 	}
 
@@ -387,23 +394,24 @@ func (h *AuthHandlers) ResendVerification(w http.ResponseWriter, r *http.Request
 	err := h.resendVerificationEmailHandler.Handle(r.Context(), cmd)
 	if err != nil {
 		if err == appErrors.ErrInvalidInput {
-			respondError(w, http.StatusBadRequest, "Invalid email")
+			respondErrorI18n(w, r, h.translator, http.StatusBadRequest, "invalid_email")
 			return
 		}
 		if err == appErrors.ErrNotFound {
-			respondError(w, http.StatusNotFound, "User not found")
+			respondErrorI18n(w, r, h.translator, http.StatusNotFound, "user_not_found")
 			return
 		}
 		if err == appErrors.ErrAlreadyExists {
-			respondError(w, http.StatusConflict, "Email already verified")
+			respondErrorI18n(w, r, h.translator, http.StatusConflict, "email_already_verified")
 			return
 		}
-		respondError(w, http.StatusInternalServerError, "Failed to send verification email")
+		respondErrorI18n(w, r, h.translator, http.StatusInternalServerError, "failed_send_verification_email")
 		return
 	}
 
+	lang := i18n.GetLanguageFromContext(r.Context())
 	respondJSON(w, http.StatusOK, map[string]string{
-		"message": "Verification email sent successfully",
+		"message": h.translator.Success(lang, "verification_email_sent"),
 	})
 }
 
@@ -432,7 +440,7 @@ type ResetPasswordRequest struct {
 func (h *AuthHandlers) ForgotPassword(w http.ResponseWriter, r *http.Request) {
 	var req ForgotPasswordRequest
 	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
-		respondError(w, http.StatusBadRequest, "Invalid request body")
+		respondErrorI18n(w, r, h.translator, http.StatusBadRequest, "invalid_request_body")
 		return
 	}
 
@@ -443,23 +451,24 @@ func (h *AuthHandlers) ForgotPassword(w http.ResponseWriter, r *http.Request) {
 	err := h.requestPasswordResetHandler.Handle(r.Context(), cmd)
 	if err != nil {
 		if err == appErrors.ErrInvalidInput {
-			respondError(w, http.StatusBadRequest, "Invalid email")
+			respondErrorI18n(w, r, h.translator, http.StatusBadRequest, "invalid_email")
 			return
 		}
 		if err == appErrors.ErrNotFound {
-			respondError(w, http.StatusNotFound, "User not found")
+			respondErrorI18n(w, r, h.translator, http.StatusNotFound, "user_not_found")
 			return
 		}
 		if err == appErrors.ErrEmailNotVerified {
-			respondError(w, http.StatusForbidden, "Please verify your email before resetting password")
+			respondErrorI18n(w, r, h.translator, http.StatusForbidden, "email_not_verified_reset")
 			return
 		}
-		respondError(w, http.StatusInternalServerError, "Failed to send reset email")
+		respondErrorI18n(w, r, h.translator, http.StatusInternalServerError, "failed_send_reset_email")
 		return
 	}
 
+	lang := i18n.GetLanguageFromContext(r.Context())
 	respondJSON(w, http.StatusOK, map[string]string{
-		"message": "Password reset email sent successfully",
+		"message": h.translator.Success(lang, "password_reset_email_sent"),
 	})
 }
 
@@ -478,7 +487,7 @@ func (h *AuthHandlers) ForgotPassword(w http.ResponseWriter, r *http.Request) {
 func (h *AuthHandlers) ResetPassword(w http.ResponseWriter, r *http.Request) {
 	var req ResetPasswordRequest
 	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
-		respondError(w, http.StatusBadRequest, "Invalid request body")
+		respondErrorI18n(w, r, h.translator, http.StatusBadRequest, "invalid_request_body")
 		return
 	}
 
@@ -490,18 +499,19 @@ func (h *AuthHandlers) ResetPassword(w http.ResponseWriter, r *http.Request) {
 	err := h.resetPasswordHandler.Handle(r.Context(), cmd)
 	if err != nil {
 		if err == appErrors.ErrInvalidInput {
-			respondError(w, http.StatusBadRequest, "Invalid or expired token, or password requirements not met")
+			respondErrorI18n(w, r, h.translator, http.StatusBadRequest, "invalid_token_or_password")
 			return
 		}
 		if err == appErrors.ErrNotFound {
-			respondError(w, http.StatusNotFound, "User not found")
+			respondErrorI18n(w, r, h.translator, http.StatusNotFound, "user_not_found")
 			return
 		}
-		respondError(w, http.StatusInternalServerError, "Failed to reset password")
+		respondErrorI18n(w, r, h.translator, http.StatusInternalServerError, "failed_reset_password")
 		return
 	}
 
+	lang := i18n.GetLanguageFromContext(r.Context())
 	respondJSON(w, http.StatusOK, map[string]string{
-		"message": "Password reset successfully",
+		"message": h.translator.Success(lang, "password_reset"),
 	})
 }

internal/infrastructure/http/habit_handlers.go

@@ -10,6 +10,7 @@ import (
 	"apocapoc-api/internal/application/commands"
 	"apocapoc-api/internal/application/queries"
 	"apocapoc-api/internal/domain/repositories"
+	"apocapoc-api/internal/i18n"
 	"apocapoc-api/internal/shared/errors"
 
 	"github.com/go-chi/chi/v5"
@@ -26,6 +27,7 @@ type HabitHandlers struct {
 	markHandler            *commands.MarkHabitHandler
 	unmarkHandler          *commands.UnmarkHabitHandler
 	userRepo               repositories.UserRepository
+	translator             *i18n.Translator
 }
 
 func NewHabitHandlers(
@@ -39,6 +41,7 @@ func NewHabitHandlers(
 	markHandler *commands.MarkHabitHandler,
 	unmarkHandler *commands.UnmarkHabitHandler,
 	userRepo repositories.UserRepository,
+	translator *i18n.Translator,
 ) *HabitHandlers {
 	return &HabitHandlers{
 		createHandler:          createHandler,
@@ -51,6 +54,7 @@ func NewHabitHandlers(
 		markHandler:            markHandler,
 		unmarkHandler:          unmarkHandler,
 		userRepo:               userRepo,
+		translator:             translator,
 	}
 }
 
@@ -70,13 +74,13 @@ func NewHabitHandlers(
 func (h *HabitHandlers) CreateHabit(w http.ResponseWriter, r *http.Request) {
 	var req CreateHabitRequest
 	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
-		respondError(w, http.StatusBadRequest, "Invalid request body")
+		respondErrorI18n(w, r, h.translator, http.StatusBadRequest, "invalid_request_body")
 		return
 	}
 
 	userID, ok := GetUserIDFromContext(r.Context())
 	if !ok {
-		respondError(w, http.StatusUnauthorized, "User not authenticated")
+		respondErrorI18n(w, r, h.translator, http.StatusUnauthorized, "user_not_authenticated")
 		return
 	}
 
@@ -99,7 +103,7 @@ func (h *HabitHandlers) CreateHabit(w http.ResponseWriter, r *http.Request) {
 			respondError(w, http.StatusBadRequest, err.Error())
 			return
 		}
-		respondError(w, http.StatusInternalServerError, "Failed to create habit")
+		respondErrorI18n(w, r, h.translator, http.StatusInternalServerError, "failed_create_habit")
 		return
 	}
 
@@ -119,7 +123,7 @@ func (h *HabitHandlers) CreateHabit(w http.ResponseWriter, r *http.Request) {
 func (h *HabitHandlers) GetUserHabits(w http.ResponseWriter, r *http.Request) {
 	userID, ok := GetUserIDFromContext(r.Context())
 	if !ok {
-		respondError(w, http.StatusUnauthorized, "User not authenticated")
+		respondErrorI18n(w, r, h.translator, http.StatusUnauthorized, "user_not_authenticated")
 		return
 	}
 
@@ -129,7 +133,7 @@ func (h *HabitHandlers) GetUserHabits(w http.ResponseWriter, r *http.Request) {
 
 	habits, err := h.getUserHabitsHandler.Handle(r.Context(), query)
 	if err != nil {
-		respondError(w, http.StatusInternalServerError, "Failed to get habits")
+		respondErrorI18n(w, r, h.translator, http.StatusInternalServerError, "failed_get_habits")
 		return
 	}
 
@@ -168,7 +172,7 @@ func (h *HabitHandlers) GetHabitByID(w http.ResponseWriter, r *http.Request) {
 
 	userID, ok := GetUserIDFromContext(r.Context())
 	if !ok {
-		respondError(w, http.StatusUnauthorized, "User not authenticated")
+		respondErrorI18n(w, r, h.translator, http.StatusUnauthorized, "user_not_authenticated")
 		return
 	}
 
@@ -180,14 +184,14 @@ func (h *HabitHandlers) GetHabitByID(w http.ResponseWriter, r *http.Request) {
 	habit, err := h.getHabitByIDHandler.Handle(r.Context(), query)
 	if err != nil {
 		if err == errors.ErrNotFound {
-			respondError(w, http.StatusNotFound, "Habit not found")
+			respondErrorI18n(w, r, h.translator, http.StatusNotFound, "habit_not_found")
 			return
 		}
 		if err == errors.ErrUnauthorized {
-			respondError(w, http.StatusForbidden, "Access denied")
+			respondErrorI18n(w, r, h.translator, http.StatusForbidden, "access_denied")
 			return
 		}
-		respondError(w, http.StatusInternalServerError, "Failed to get habit")
+		respondErrorI18n(w, r, h.translator, http.StatusInternalServerError, "failed_get_habit")
 		return
 	}
 
@@ -226,13 +230,13 @@ func (h *HabitHandlers) UpdateHabit(w http.ResponseWriter, r *http.Request) {
 
 	userID, ok := GetUserIDFromContext(r.Context())
 	if !ok {
-		respondError(w, http.StatusUnauthorized, "User not authenticated")
+		respondErrorI18n(w, r, h.translator, http.StatusUnauthorized, "user_not_authenticated")
 		return
 	}
 
 	var req UpdateHabitRequest
 	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
-		respondError(w, http.StatusBadRequest, "Invalid request body")
+		respondErrorI18n(w, r, h.translator, http.StatusBadRequest, "invalid_request_body")
 		return
 	}
 
@@ -249,18 +253,18 @@ func (h *HabitHandlers) UpdateHabit(w http.ResponseWriter, r *http.Request) {
 
 	if err := h.updateHandler.Handle(r.Context(), cmd); err != nil {
 		if err == errors.ErrNotFound {
-			respondError(w, http.StatusNotFound, "Habit not found")
+			respondErrorI18n(w, r, h.translator, http.StatusNotFound, "habit_not_found")
 			return
 		}
 		if err == errors.ErrUnauthorized {
-			respondError(w, http.StatusForbidden, "Access denied")
+			respondErrorI18n(w, r, h.translator, http.StatusForbidden, "access_denied")
 			return
 		}
 		if err == errors.ErrInvalidInput {
-			respondError(w, http.StatusBadRequest, "Invalid input")
+			respondErrorI18n(w, r, h.translator, http.StatusBadRequest, "invalid_input")
 			return
 		}
-		respondError(w, http.StatusInternalServerError, "Failed to update habit")
+		respondErrorI18n(w, r, h.translator, http.StatusInternalServerError, "failed_update_habit")
 		return
 	}
 
@@ -285,7 +289,7 @@ func (h *HabitHandlers) ArchiveHabit(w http.ResponseWriter, r *http.Request) {
 
 	userID, ok := GetUserIDFromContext(r.Context())
 	if !ok {
-		respondError(w, http.StatusUnauthorized, "User not authenticated")
+		respondErrorI18n(w, r, h.translator, http.StatusUnauthorized, "user_not_authenticated")
 		return
 	}
 
@@ -296,14 +300,14 @@ func (h *HabitHandlers) ArchiveHabit(w http.ResponseWriter, r *http.Request) {
 
 	if err := h.archiveHandler.Handle(r.Context(), cmd); err != nil {
 		if err == errors.ErrNotFound {
-			respondError(w, http.StatusNotFound, "Habit not found")
+			respondErrorI18n(w, r, h.translator, http.StatusNotFound, "habit_not_found")
 			return
 		}
 		if err == errors.ErrUnauthorized {
-			respondError(w, http.StatusForbidden, "Access denied")
+			respondErrorI18n(w, r, h.translator, http.StatusForbidden, "access_denied")
 			return
 		}
-		respondError(w, http.StatusInternalServerError, "Failed to archive habit")
+		respondErrorI18n(w, r, h.translator, http.StatusInternalServerError, "failed_archive_habit")
 		return
 	}
 
@@ -333,7 +337,7 @@ func (h *HabitHandlers) GetHabitEntries(w http.ResponseWriter, r *http.Request)
 
 	userID, ok := GetUserIDFromContext(r.Context())
 	if !ok {
-		respondError(w, http.StatusUnauthorized, "User not authenticated")
+		respondErrorI18n(w, r, h.translator, http.StatusUnauthorized, "user_not_authenticated")
 		return
 	}
 
@@ -345,7 +349,7 @@ func (h *HabitHandlers) GetHabitEntries(w http.ResponseWriter, r *http.Request)
 	if fromStr := r.URL.Query().Get("from"); fromStr != "" {
 		from, err := time.Parse("2006-01-02", fromStr)
 		if err != nil {
-			respondError(w, http.StatusBadRequest, "Invalid 'from' date format (use YYYY-MM-DD)")
+			respondErrorI18n(w, r, h.translator, http.StatusBadRequest, "invalid_from_date_format")
 			return
 		}
 		query.From = &from
@@ -354,7 +358,7 @@ func (h *HabitHandlers) GetHabitEntries(w http.ResponseWriter, r *http.Request)
 	if toStr := r.URL.Query().Get("to"); toStr != "" {
 		to, err := time.Parse("2006-01-02", toStr)
 		if err != nil {
-			respondError(w, http.StatusBadRequest, "Invalid 'to' date format (use YYYY-MM-DD)")
+			respondErrorI18n(w, r, h.translator, http.StatusBadRequest, "invalid_to_date_format")
 			return
 		}
 		query.To = &to
@@ -375,7 +379,7 @@ func (h *HabitHandlers) GetHabitEntries(w http.ResponseWriter, r *http.Request)
 	if pageStr := r.URL.Query().Get("page"); pageStr != "" {
 		page, err := strconv.Atoi(pageStr)
 		if err != nil || page < 1 {
-			respondError(w, http.StatusBadRequest, "Invalid 'page' parameter")
+			respondErrorI18n(w, r, h.translator, http.StatusBadRequest, "invalid_page_parameter")
 			return
 		}
 		query.Page = page
@@ -386,7 +390,7 @@ func (h *HabitHandlers) GetHabitEntries(w http.ResponseWriter, r *http.Request)
 	if limitStr := r.URL.Query().Get("limit"); limitStr != "" {
 		limit, err := strconv.Atoi(limitStr)
 		if err != nil || limit < 1 || limit > 100 {
-			respondError(w, http.StatusBadRequest, "Invalid 'limit' parameter (must be 1-100)")
+			respondErrorI18n(w, r, h.translator, http.StatusBadRequest, "invalid_limit_parameter")
 			return
 		}
 		query.Limit = limit
@@ -402,14 +406,14 @@ func (h *HabitHandlers) GetHabitEntries(w http.ResponseWriter, r *http.Request)
 	result, err := h.getHabitEntriesHandler.Handle(r.Context(), query)
 	if err != nil {
 		if err == errors.ErrNotFound {
-			respondError(w, http.StatusNotFound, "Habit not found")
+			respondErrorI18n(w, r, h.translator, http.StatusNotFound, "habit_not_found")
 			return
 		}
 		if err == errors.ErrUnauthorized {
-			respondError(w, http.StatusForbidden, "Access denied")
+			respondErrorI18n(w, r, h.translator, http.StatusForbidden, "access_denied")
 			return
 		}
-		respondError(w, http.StatusInternalServerError, "Failed to get habit entries")
+		respondErrorI18n(w, r, h.translator, http.StatusInternalServerError, "failed_get_habit_entries")
 		return
 	}
 
@@ -447,13 +451,13 @@ func (h *HabitHandlers) GetHabitEntries(w http.ResponseWriter, r *http.Request)
 func (h *HabitHandlers) GetTodaysHabits(w http.ResponseWriter, r *http.Request) {
 	userID, ok := GetUserIDFromContext(r.Context())
 	if !ok {
-		respondError(w, http.StatusUnauthorized, "User not authenticated")
+		respondErrorI18n(w, r, h.translator, http.StatusUnauthorized, "user_not_authenticated")
 		return
 	}
 
 	user, err := h.userRepo.FindByID(r.Context(), userID)
 	if err != nil {
-		respondError(w, http.StatusInternalServerError, "Failed to get user")
+		respondErrorI18n(w, r, h.translator, http.StatusInternalServerError, "failed_get_user")
 		return
 	}
 
@@ -473,7 +477,7 @@ func (h *HabitHandlers) GetTodaysHabits(w http.ResponseWriter, r *http.Request)
 
 	habits, err := h.getTodaysHandler.Handle(r.Context(), query)
 	if err != nil {
-		respondError(w, http.StatusInternalServerError, "Failed to get habits")
+		respondErrorI18n(w, r, h.translator, http.StatusInternalServerError, "failed_get_habits")
 		return
 	}
 
@@ -523,13 +527,13 @@ func (h *HabitHandlers) MarkHabit(w http.ResponseWriter, r *http.Request) {
 
 	var req MarkHabitRequest
 	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
-		respondError(w, http.StatusBadRequest, "Invalid request body")
+		respondErrorI18n(w, r, h.translator, http.StatusBadRequest, "invalid_request_body")
 		return
 	}
 
 	scheduledDate, err := time.Parse("2006-01-02", req.ScheduledDate)
 	if err != nil {
-		respondError(w, http.StatusBadRequest, "Invalid date format (use YYYY-MM-DD)")
+		respondErrorI18n(w, r, h.translator, http.StatusBadRequest, "invalid_date_format")
 		return
 	}
 
@@ -541,14 +545,14 @@ func (h *HabitHandlers) MarkHabit(w http.ResponseWriter, r *http.Request) {
 
 	if err := h.markHandler.Handle(r.Context(), cmd); err != nil {
 		if err == errors.ErrAlreadyExists {
-			respondError(w, http.StatusConflict, "Habit already marked for this date")
+			respondErrorI18n(w, r, h.translator, http.StatusConflict, "habit_already_marked")
 			return
 		}
 		if err == errors.ErrNotFound {
-			respondError(w, http.StatusNotFound, "Habit not found")
+			respondErrorI18n(w, r, h.translator, http.StatusNotFound, "habit_not_found")
 			return
 		}
-		respondError(w, http.StatusInternalServerError, "Failed to mark habit")
+		respondErrorI18n(w, r, h.translator, http.StatusInternalServerError, "failed_mark_habit")
 		return
 	}
 
@@ -576,13 +580,13 @@ func (h *HabitHandlers) UnmarkHabit(w http.ResponseWriter, r *http.Request) {
 
 	userID, ok := GetUserIDFromContext(r.Context())
 	if !ok {
-		respondError(w, http.StatusUnauthorized, "User not authenticated")
+		respondErrorI18n(w, r, h.translator, http.StatusUnauthorized, "user_not_authenticated")
 		return
 	}
 
 	scheduledDate, err := time.Parse("2006-01-02", dateStr)
 	if err != nil {
-		respondError(w, http.StatusBadRequest, "Invalid date format (use YYYY-MM-DD)")
+		respondErrorI18n(w, r, h.translator, http.StatusBadRequest, "invalid_date_format")
 		return
 	}
 
@@ -594,14 +598,14 @@ func (h *HabitHandlers) UnmarkHabit(w http.ResponseWriter, r *http.Request) {
 
 	if err := h.unmarkHandler.Handle(r.Context(), cmd); err != nil {
 		if err == errors.ErrNotFound {
-			respondError(w, http.StatusNotFound, "Habit entry not found")
+			respondErrorI18n(w, r, h.translator, http.StatusNotFound, "habit_entry_not_found")
 			return
 		}
 		if err == errors.ErrUnauthorized {
-			respondError(w, http.StatusForbidden, "Access denied")
+			respondErrorI18n(w, r, h.translator, http.StatusForbidden, "access_denied")
 			return
 		}
-		respondError(w, http.StatusInternalServerError, "Failed to unmark habit")
+		respondErrorI18n(w, r, h.translator, http.StatusInternalServerError, "failed_unmark_habit")
 		return
 	}
 

internal/infrastructure/http/i18n_helper.go

@@ -0,0 +1,52 @@
+package http
+
+import (
+	"net/http"
+	"strings"
+
+	"apocapoc-api/internal/i18n"
+
+	"golang.org/x/text/language"
+)
+
+func respondErrorI18n(w http.ResponseWriter, r *http.Request, translator *i18n.Translator, status int, key string) {
+	lang := i18n.GetLanguageFromContext(r.Context())
+	message := translator.Error(lang, key)
+	respondJSON(w, status, ErrorResponse{Error: message})
+}
+
+func respondSuccessI18n(w http.ResponseWriter, r *http.Request, translator *i18n.Translator, key string) {
+	lang := i18n.GetLanguageFromContext(r.Context())
+	message := translator.Success(lang, key)
+	respondJSON(w, http.StatusOK, map[string]string{"message": message})
+}
+
+func respondValidationErrorI18n(w http.ResponseWriter, r *http.Request, translator *i18n.Translator, err error) {
+	lang := i18n.GetLanguageFromContext(r.Context())
+	errMsg := err.Error()
+	var field string
+	var translatedMsg string
+
+	if strings.Contains(errMsg, ": ") {
+		parts := strings.SplitN(errMsg, ": ", 3)
+		if len(parts) >= 3 {
+			field = parts[1]
+			validationKey := parts[2]
+			translatedMsg = translator.Validation(lang, validationKey)
+			respondJSON(w, http.StatusBadRequest, ValidationErrorResponse{
+				Error: translatedMsg,
+				Field: field,
+			})
+			return
+		}
+	}
+
+	respondJSON(w, http.StatusBadRequest, ErrorResponse{
+		Error: errMsg,
+	})
+}
+
+func getLanguageFromRequest(r *http.Request, translator *i18n.Translator) language.Tag {
+	lang := i18n.GetLanguageFromContext(r.Context())
+	return lang
+}

internal/infrastructure/http/integration_test.go

@@ -11,6 +11,7 @@ import (
 
 	"apocapoc-api/internal/application/commands"
 	"apocapoc-api/internal/application/queries"
+	"apocapoc-api/internal/i18n"
 	"apocapoc-api/internal/infrastructure/auth"
 	"apocapoc-api/internal/infrastructure/crypto"
 	"apocapoc-api/internal/infrastructure/persistence/sqlite"
@@ -66,13 +67,15 @@ func setupTestServer(t *testing.T) *TestServer {
 
 	deleteUserHandler := commands.NewDeleteUserHandler(userRepo)
 
-	authHandlers := NewAuthHandlers(registerHandler, loginHandler, refreshTokenHandler, revokeTokenHandler, revokeAllTokensHandler, verifyEmailHandler, resendVerificationEmailHandler, requestPasswordResetHandler, resetPasswordHandler, jwtService, refreshTokenRepo, refreshTokenExpiry)
+	translator, _ := i18n.NewTranslator()
-	habitHandlers := NewHabitHandlers(createHandler, getTodaysHandler, getUserHabitsHandler, getHabitByIDHandler, getHabitEntriesHandler, updateHandler, archiveHandler, markHandler, unmarkHandler, userRepo)
-	statsHandlers := NewStatsHandlers(getHabitStatsHandler)
-	healthHandlers := NewHealthHandlers(db)
-	userHandlers := NewUserHandlers(deleteUserHandler)
 
-	router := NewRouter("http://localhost:3000", habitHandlers, authHandlers, statsHandlers, healthHandlers, userHandlers, jwtService)
+	authHandlers := NewAuthHandlers(registerHandler, loginHandler, refreshTokenHandler, revokeTokenHandler, revokeAllTokensHandler, verifyEmailHandler, resendVerificationEmailHandler, requestPasswordResetHandler, resetPasswordHandler, jwtService, refreshTokenRepo, refreshTokenExpiry, translator)
+	habitHandlers := NewHabitHandlers(createHandler, getTodaysHandler, getUserHabitsHandler, getHabitByIDHandler, getHabitEntriesHandler, updateHandler, archiveHandler, markHandler, unmarkHandler, userRepo, translator)
+	statsHandlers := NewStatsHandlers(getHabitStatsHandler, translator)
+	healthHandlers := NewHealthHandlers(db)
+	userHandlers := NewUserHandlers(deleteUserHandler, translator)
+
+	router := NewRouter("http://localhost:3000", habitHandlers, authHandlers, statsHandlers, healthHandlers, userHandlers, jwtService, translator)
 
 	handler := http.Handler(router)
 	return &TestServer{

internal/infrastructure/http/router.go

@@ -4,6 +4,7 @@ import (
 	"net/http"
 	"time"
 
+	"apocapoc-api/internal/i18n"
 	"apocapoc-api/internal/infrastructure/auth"
 
 	"github.com/go-chi/chi/v5"
@@ -15,15 +16,16 @@ import (
 	_ "apocapoc-api/docs"
 )
 
-func NewRouter(appURL string, habitHandlers *HabitHandlers, authHandlers *AuthHandlers, statsHandlers *StatsHandlers, healthHandlers *HealthHandlers, userHandlers *UserHandlers, jwtService *auth.JWTService) *chi.Mux {
+func NewRouter(appURL string, habitHandlers *HabitHandlers, authHandlers *AuthHandlers, statsHandlers *StatsHandlers, healthHandlers *HealthHandlers, userHandlers *UserHandlers, jwtService *auth.JWTService, translator *i18n.Translator) *chi.Mux {
 	r := chi.NewRouter()
 
 	r.Use(middleware.Logger)
 	r.Use(middleware.Recoverer)
+	r.Use(i18n.LanguageMiddleware(translator))
 	r.Use(cors.Handler(cors.Options{
 		AllowedOrigins:   []string{appURL},
 		AllowedMethods:   []string{"GET", "POST", "PUT", "DELETE", "OPTIONS"},
-		AllowedHeaders:   []string{"Accept", "Authorization", "Content-Type"},
+		AllowedHeaders:   []string{"Accept", "Authorization", "Content-Type", "Accept-Language"},
 		AllowCredentials: true,
 	}))
 

internal/infrastructure/http/stats_handlers.go

@@ -6,18 +6,22 @@ import (
 	"apocapoc-api/internal/application/queries"
 	"apocapoc-api/internal/shared/errors"
 
+	"apocapoc-api/internal/i18n"
 	"github.com/go-chi/chi/v5"
 )
 
 type StatsHandlers struct {
 	getHabitStatsHandler *queries.GetHabitStatsHandler
+	translator           *i18n.Translator
 }
 
 func NewStatsHandlers(
 	getHabitStatsHandler *queries.GetHabitStatsHandler,
+	translator *i18n.Translator,
 ) *StatsHandlers {
 	return &StatsHandlers{
 		getHabitStatsHandler: getHabitStatsHandler,
+		translator:           translator,
 	}
 }
 
@@ -39,7 +43,7 @@ func (h *StatsHandlers) GetHabitStats(w http.ResponseWriter, r *http.Request) {
 
 	userID, ok := GetUserIDFromContext(r.Context())
 	if !ok {
-		respondError(w, http.StatusUnauthorized, "User not authenticated")
+		respondErrorI18n(w, r, h.translator, http.StatusUnauthorized, "user_not_authenticated")
 		return
 	}
 
@@ -51,14 +55,14 @@ func (h *StatsHandlers) GetHabitStats(w http.ResponseWriter, r *http.Request) {
 	stats, err := h.getHabitStatsHandler.Handle(r.Context(), query)
 	if err != nil {
 		if err == errors.ErrNotFound {
-			respondError(w, http.StatusNotFound, "Habit not found")
+			respondErrorI18n(w, r, h.translator, http.StatusNotFound, "habit_not_found")
 			return
 		}
 		if err == errors.ErrUnauthorized {
-			respondError(w, http.StatusForbidden, "Access denied")
+			respondErrorI18n(w, r, h.translator, http.StatusForbidden, "access_denied")
 			return
 		}
-		respondError(w, http.StatusInternalServerError, "Failed to get habit stats")
+		respondErrorI18n(w, r, h.translator, http.StatusInternalServerError, "failed_get_stats")
 		return
 	}
 

internal/infrastructure/http/user_handlers.go

@@ -4,16 +4,19 @@ import (
 	"net/http"
 
 	"apocapoc-api/internal/application/commands"
+	"apocapoc-api/internal/i18n"
 	"apocapoc-api/internal/shared/errors"
 )
 
 type UserHandlers struct {
 	deleteUserHandler *commands.DeleteUserHandler
+	translator        *i18n.Translator
 }
 
-func NewUserHandlers(deleteUserHandler *commands.DeleteUserHandler) *UserHandlers {
+func NewUserHandlers(deleteUserHandler *commands.DeleteUserHandler, translator *i18n.Translator) *UserHandlers {
 	return &UserHandlers{
 		deleteUserHandler: deleteUserHandler,
+		translator:        translator,
 	}
 }
 
@@ -38,14 +41,15 @@ func (h *UserHandlers) DeleteAccount(w http.ResponseWriter, r *http.Request) {
 	err := h.deleteUserHandler.Handle(r.Context(), cmd)
 	if err != nil {
 		if err == errors.ErrNotFound {
-			respondError(w, http.StatusNotFound, "User not found")
+			respondErrorI18n(w, r, h.translator, http.StatusNotFound, "user_not_found")
 			return
 		}
-		respondError(w, http.StatusInternalServerError, "Failed to delete account")
+		respondErrorI18n(w, r, h.translator, http.StatusInternalServerError, "failed_delete_user")
 		return
 	}
 
+	lang := i18n.GetLanguageFromContext(r.Context())
 	respondJSON(w, http.StatusOK, map[string]string{
-		"message": "Account deleted successfully",
+		"message": h.translator.Success(lang, "user_deleted"),
 	})
 }