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_test.go

@@ -0,0 +1,116 @@
+package localization
+
+import (
+	"encoding/json"
+	"sort"
+	"testing"
+
+	"github.com/nicksnyder/go-i18n/v2/i18n"
+)
+
+func TestLocalizationService(t *testing.T) {
+	service := NewLocalizationService()
+
+	t.Run("English localization", func(t *testing.T) {
+		localizer := service.GetLocalizer("en")
+		result := localizer.MustLocalize(&i18n.LocalizeConfig{MessageID: "loading"})
+		if result != "Loading..." {
+			t.Errorf("Expected 'Loading...', got '%s'", result)
+		}
+	})
+
+	t.Run("French localization", func(t *testing.T) {
+		localizer := service.GetLocalizer("fr")
+		result := localizer.MustLocalize(&i18n.LocalizeConfig{MessageID: "loading"})
+		if result != "Chargement..." {
+			t.Errorf("Expected 'Chargement...', got '%s'", result)
+		}
+	})
+
+	t.Run("All required keys exist in English", func(t *testing.T) {
+		localizer := service.GetLocalizer("en")
+		requiredKeys := []string{
+			"loading", "why_am_i_seeing", "protected_by", "made_with",
+			"mascot_design", "try_again", "go_home", "javascript_required",
+		}
+
+		for _, key := range requiredKeys {
+			result := localizer.MustLocalize(&i18n.LocalizeConfig{MessageID: key})
+			if result == "" {
+				t.Errorf("Key '%s' returned empty string", key)
+			}
+		}
+	})
+
+	t.Run("All required keys exist in French", func(t *testing.T) {
+		localizer := service.GetLocalizer("fr")
+		requiredKeys := []string{
+			"loading", "why_am_i_seeing", "protected_by", "made_with",
+			"mascot_design", "try_again", "go_home", "javascript_required",
+		}
+
+		for _, key := range requiredKeys {
+			result := localizer.MustLocalize(&i18n.LocalizeConfig{MessageID: key})
+			if result == "" {
+				t.Errorf("Key '%s' returned empty string", key)
+			}
+		}
+	})
+}
+
+type manifest struct {
+	SupportedLanguages []string `json:"supported_languages"`
+}
+
+func loadManifest(t *testing.T) manifest {
+	t.Helper()
+
+	fin, err := localeFS.Open("locales/manifest.json")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer fin.Close()
+
+	var result manifest
+	if err := json.NewDecoder(fin).Decode(&result); err != nil {
+		t.Fatal(err)
+	}
+
+	return result
+}
+
+func TestComprehensiveTranslations(t *testing.T) {
+	service := NewLocalizationService()
+
+	var translations = map[string]any{}
+	fin, err := localeFS.Open("locales/en.json")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer fin.Close()
+
+	if err := json.NewDecoder(fin).Decode(&translations); err != nil {
+		t.Fatal(err)
+	}
+
+	var keys []string
+	for k := range translations {
+		keys = append(keys, k)
+	}
+
+	sort.Strings(keys)
+
+	for _, lang := range loadManifest(t).SupportedLanguages {
+		t.Run(lang, func(t *testing.T) {
+			loc := service.GetLocalizer(lang)
+			sl := SimpleLocalizer{Localizer: loc}
+			for _, key := range keys {
+				t.Run(key, func(t *testing.T) {
+					if result := sl.T(key); result == "" {
+						t.Error("key not defined")
+					}
+				})
+			}
+		})
+	}
+}