feat: implement localization system (#716)

* lib/localization: implement localization system

Locale files are placed in lib/localization/locales/. If you add a
locale, update manifest.json with available locales.

* Exclude locales from check spelling

* tests(lib/localization): add comprehensive translations test

Signed-off-by: Xe Iaso <me@xeiaso.net>

* fix(challenge/metarefresh): enable localization

Signed-off-by: Xe Iaso <me@xeiaso.net>

* fix: use simple syntax for localization in templ

Also localize CELPHASE into French according to the wishes of the
artist.

Signed-off-by: Xe Iaso <me@xeiaso.net>

* chore: spelling

Signed-off-by: Xe Iaso <me@xeiaso.net>

* chore:(js): fix forbidden patterns

Signed-off-by: Xe Iaso <me@xeiaso.net>

* chore: add goi18n to tools

Signed-off-by: Xe Iaso <me@xeiaso.net>

* test(lib/localization): dynamically determine the list of supported languages

Signed-off-by: Xe Iaso <me@xeiaso.net>

---------

Signed-off-by: Xe Iaso <me@xeiaso.net>
Co-authored-by: Xe Iaso <me@xeiaso.net>

lib/localization/localization.go

@@ -0,0 +1,100 @@
+package localization
+
+import (
+	"embed"
+	"encoding/json"
+	"net/http"
+	"strings"
+	"sync"
+
+	"github.com/nicksnyder/go-i18n/v2/i18n"
+	"golang.org/x/text/language"
+)
+
+//go:embed locales/*.json
+var localeFS embed.FS
+
+type LocalizationService struct {
+	bundle *i18n.Bundle
+}
+
+var (
+	globalService *LocalizationService
+	once          sync.Once
+)
+
+func NewLocalizationService() *LocalizationService {
+	once.Do(func() {
+		bundle := i18n.NewBundle(language.English)
+		bundle.RegisterUnmarshalFunc("json", json.Unmarshal)
+
+		// Read all JSON files from the locales directory
+		entries, err := localeFS.ReadDir("locales")
+		if err != nil {
+			// Try fallback - create a minimal service with default messages
+			globalService = &LocalizationService{bundle: bundle}
+			return
+		}
+
+		loadedAny := false
+		for _, entry := range entries {
+			if !entry.IsDir() && strings.HasSuffix(entry.Name(), ".json") {
+				filePath := "locales/" + entry.Name()
+				_, err := bundle.LoadMessageFileFS(localeFS, filePath)
+				if err != nil {
+					// Log error but continue with other files
+					continue
+				}
+				loadedAny = true
+			}
+		}
+
+		if !loadedAny {
+			// If no files were loaded successfully, create minimal service
+			globalService = &LocalizationService{bundle: bundle}
+			return
+		}
+
+		globalService = &LocalizationService{bundle: bundle}
+	})
+	
+	// Safety check - if globalService is still nil, create a minimal one
+	if globalService == nil {
+		bundle := i18n.NewBundle(language.English)
+		bundle.RegisterUnmarshalFunc("json", json.Unmarshal)
+		globalService = &LocalizationService{bundle: bundle}
+	}
+	
+	return globalService
+}
+
+func (ls *LocalizationService) GetLocalizer(lang string) *i18n.Localizer {
+	return i18n.NewLocalizer(ls.bundle, lang)
+}
+
+func (ls *LocalizationService) GetLocalizerFromRequest(r *http.Request) *i18n.Localizer {
+	if ls == nil || ls.bundle == nil {
+		// Fallback to a basic bundle if service is not properly initialized
+		bundle := i18n.NewBundle(language.English)
+		bundle.RegisterUnmarshalFunc("json", json.Unmarshal)
+		return i18n.NewLocalizer(bundle, "en")
+	}
+	acceptLanguage := r.Header.Get("Accept-Language")
+	return i18n.NewLocalizer(ls.bundle, acceptLanguage, "en")
+}
+
+// SimpleLocalizer wraps i18n.Localizer with a more convenient API
+type SimpleLocalizer struct {
+	Localizer *i18n.Localizer
+}
+
+// T provides a concise way to localize messages
+func (sl *SimpleLocalizer) T(messageID string) string {
+	return sl.Localizer.MustLocalize(&i18n.LocalizeConfig{MessageID: messageID})
+}
+
+// GetLocalizer creates a localizer based on the request's Accept-Language header
+func GetLocalizer(r *http.Request) *SimpleLocalizer {
+	localizer := NewLocalizationService().GetLocalizerFromRequest(r)
+	return &SimpleLocalizer{Localizer: localizer}
+}