feat: Implement i18n infrastructure

frontend/LanguageContext.tsx

@@ -0,0 +1,63 @@
+import React, { createContext, useContext, useEffect, useState, ReactNode } from 'react';
+import { translations, Language } from './translations';
+
+interface LanguageContextProps {
+  language: Language;
+  setLanguage: (lang: Language) => void;
+  t: (path: string, params?: Record<string, string | number>) => string;
+}
+
+const LanguageContext = createContext<LanguageContextProps | undefined>(undefined);
+
+export const LanguageProvider: React.FC<{ children: ReactNode }> = ({ children }) => {
+  const [language, setLanguageState] = useState<Language>('en');
+
+  useEffect(() => {
+    const savedLang = localStorage.getItem('plexsync-language') as Language;
+    if (savedLang && translations[savedLang]) {
+      setLanguageState(savedLang);
+    }
+  }, []);
+
+  const setLanguage = (lang: Language) => {
+    setLanguageState(lang);
+    localStorage.setItem('plexsync-language', lang);
+  };
+
+  const t = (path: string, params?: Record<string, string | number>): string => {
+    const keys = path.split('.');
+    let current: any = translations[language];
+
+    for (const key of keys) {
+      if (current[key] === undefined) {
+        console.warn(`Missing translation for key: ${path} in language: ${language}`);
+        return path;
+      }
+      current = current[key];
+    }
+
+    let text = current as string;
+
+    if (params) {
+      Object.entries(params).forEach(([key, value]) => {
+        text = text.replace(`{${key}}`, String(value));
+      });
+    }
+
+    return text;
+  };
+
+  return (
+    <LanguageContext.Provider value={{ language, setLanguage, t }}>
+      {children}
+    </LanguageContext.Provider>
+  );
+};
+
+export const useLanguage = () => {
+  const context = useContext(LanguageContext);
+  if (!context) {
+    throw new Error('useLanguage must be used within a LanguageProvider');
+  }
+  return context;
+};