feat(frontend): add multi-language support (en, zh-Hans, zh-Hant, ja)

frontend/lib/l10n/app_en.arb

@@ -0,0 +1,70 @@
+{
+  "@@locale": "en",
+  "settings": "Settings",
+  "networkConfiguration": "Network Configuration",
+  "backendServerUrl": "Backend Server URL",
+  "saveNetworkSettings": "Save Network Settings",
+  "serverUrlUpdated": "Server URL Updated",
+  "themeCustomization": "Theme Customization",
+  "appearanceMode": "Appearance Mode",
+  "system": "System",
+  "light": "Light",
+  "dark": "Dark",
+  "accentColor": "Accent Color",
+  "explore": "Explore",
+  "livePreviewThumbnails": "Live Preview Thumbnails",
+  "livePreviewThumbnailsDesc": "Show cached snapshot covers for live rooms when available.",
+  "security": "Security",
+  "oldPassword": "Old Password",
+  "newPassword": "New Password",
+  "changePassword": "Change Password",
+  "logout": "Logout",
+  "confirmLogout": "Confirm Logout",
+  "confirmLogoutDesc": "Are you sure you want to log out now?",
+  "cancel": "Cancel",
+  "language": "Language",
+  "selectLanguage": "Select Language",
+  "english": "English",
+  "simplifiedChinese": "简体中文",
+  "traditionalChinese": "繁體中文",
+  "japanese": "日本語",
+  "console": "Console",
+  "failedToLoadRooms": "Failed to load rooms",
+  "goLive": "Go Live",
+  "noActiveRooms": "No active rooms. Be the first!",
+  "hostId": "Host ID",
+  "username": "Username",
+  "password": "Password",
+  "fillAllFields": "Please fill in all fields",
+  "networkError": "Network Error: Could not connect to server",
+  "loginFailed": "Login Failed",
+  "login": "LOGIN",
+  "dontHaveAccount": "Don't have an account? Create one",
+  "createAccount": "Create Account",
+  "joinHightube": "Join Hightube",
+  "desiredUsername": "Desired Username",
+  "register": "REGISTER",
+  "alreadyHaveAccount": "Already have an account? Login here",
+  "accountCreated": "Account created! Please login.",
+  "playbackResolution": "Playback Resolution",
+  "availableNow": "Available now",
+  "waitingForTranscoding": "Waiting for backend transcoding output",
+  "sendMessage": "Send a message...",
+  "liveChat": "Live Chat",
+  "refresh": "Refresh",
+  "volume": "Volume",
+  "danmakuOn": "Danmaku On",
+  "danmakuOff": "Danmaku Off",
+  "fullscreen": "Fullscreen",
+  "exitFullscreen": "Exit Fullscreen",
+  "resolution": "Resolution",
+  "playbackOptionsDesc": "Select an available transcoded stream.",
+  "sourceOnlyDesc": "Only the source stream is available right now.",
+  "myStreamConsole": "My Stream Console",
+  "noRoomInfo": "No room info found.",
+  "roomTitle": "Room Title",
+  "rtmpServerUrl": "RTMP Server URL",
+  "streamKey": "Stream Key (Keep Secret!)",
+  "copiedToClipboard": "Copied to clipboard",
+  "failedToFetchRoomInfo": "Failed to fetch room info"
+}