chore: build

frontend/src/i18n/LanguageContext.tsx

@@ -0,0 +1,46 @@
+import { createContext, useCallback, useContext, useMemo, useState, type ReactNode } from "react";
+import { LOCALES, translate, type Locale, type MessageKey } from "./messages";
+
+const STORAGE_KEY = "ui_locale";
+
+function detectInitialLocale(): Locale {
+  const stored = localStorage.getItem(STORAGE_KEY);
+  if (stored && (LOCALES as string[]).includes(stored)) return stored as Locale;
+
+  const browser = navigator.language?.slice(0, 2);
+  if (browser && (LOCALES as string[]).includes(browser)) return browser as Locale;
+
+  return "en";
+}
+
+interface LanguageContextValue {
+  locale: Locale;
+  setLocale: (locale: Locale) => void;
+  t: (key: MessageKey, vars?: Record<string, string | number>) => string;
+}
+
+const LanguageContext = createContext<LanguageContextValue | undefined>(undefined);
+
+export function LanguageProvider({ children }: { children: ReactNode }) {
+  const [locale, setLocaleState] = useState<Locale>(detectInitialLocale);
+
+  const setLocale = useCallback((next: Locale) => {
+    setLocaleState(next);
+    localStorage.setItem(STORAGE_KEY, next);
+  }, []);
+
+  const t = useCallback(
+    (key: MessageKey, vars?: Record<string, string | number>) => translate(locale, key, vars),
+    [locale],
+  );
+
+  const value = useMemo(() => ({ locale, setLocale, t }), [locale, setLocale, t]);
+
+  return <LanguageContext.Provider value={value}>{children}</LanguageContext.Provider>;
+}
+
+export function useI18n(): LanguageContextValue {
+  const ctx = useContext(LanguageContext);
+  if (!ctx) throw new Error("useI18n must be used within a LanguageProvider");
+  return ctx;
+}