Apply i18n to all UI components with ko/ja translations

- Add src/i18n/i18n.ts translation engine (ported from SimpleDeckyTDP)
- Add defaults/i18n/{ko,ja,template}.json with 80 translation keys
- Add defaults/i18n/language_metadata.json and steam_language_map.json
- Add scripts/build_i18n_json.sh to generate languages.json
- Apply t() to all 10 components: Content, ConfigurationSection,
  FlatpaksModal, FpsMultiplierControl, InstallationButton, NerdStuffModal,
  ProfileManagement, SmartClipboardButton, FgmodClipboardButton, UsageInstructions

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

1 files changed, 65 insertions, 0 deletions

diff --git a/src/i18n/i18n.ts b/src/i18n/i18n.ts
new file mode 100644
index 0000000..83ed3da
--- /dev/null
+++ b/src/i18n/i18n.ts
@@ -0,0 +1,65 @@
+// languages.json build via CI build
+// to generate for localhost/dev, run `build_i18n_json.sh` script
+import * as languages from "./languages.json";
+
+function getLangs() {
+  const langs = languages.language_metadata;
+
+  Object.keys(languages).map((lang) => {
+    if (lang === "language_metadata" || lang == "steam_language_map") {
+      return;
+    }
+    const strs = languages[lang];
+    if (lang && strs && langs[lang]?.name) {
+      langs[lang].strings = strs;
+    }
+  });
+
+  return langs;
+}
+
+export const LANGS: {
+  [key: string]: {
+    name: string;
+    strings: {
+      [key: string]: string;
+    };
+  };
+} = getLangs();
+
+let cachedLang: string | undefined;
+
+export const getCurrentLanguage = (): string => {
+  if (cachedLang) return cachedLang;
+
+  const lang = window.LocalizationManager.m_rgLocalesToUse[0];
+  cachedLang = lang;
+  return lang;
+};
+
+export const getLanguageName = (lang?: string): string => {
+  const targetLang = lang || getCurrentLanguage();
+  return LANGS[targetLang]?.name || targetLang;
+};
+
+/**
+ * Translate a key to the current language
+ *
+ * @param key - Translation key
+ * @param originalString - Original text (fallback)
+ * @returns Translated string or original text if translation not found
+ *
+ * @example
+ * t('CONTENT_FPS_MULTIPLIER', 'FPS Multiplier')
+ */
+const t = (key: string, originalString: string): string => {
+  const lang = getCurrentLanguage();
+
+  // English always returns the original text
+  if (lang === "en") return originalString;
+
+  // Return translation if exists, otherwise return original text
+  return LANGS[lang]?.strings?.[key] ?? originalString;
+};
+
+export default t;