Configure web display language from profile settings, default is set to

src/app/[locale]/dashboard/profile/page.tsx

@@ -1,6 +1,6 @@
 'use client';
 
-import { useState } from 'react';
+import { useState, useEffect } from 'react';
 import { Button } from '@/components/ui/button';
 import { Card, CardContent, CardDescription, CardFooter, CardHeader, CardTitle } from '@/components/ui/card';
 import { Input } from '@/components/ui/input';
@@ -9,7 +9,8 @@ import { Avatar, AvatarFallback, AvatarImage } from '@/components/ui/avatar';
 import { Save } from 'lucide-react';
 import { useToast } from '@/hooks/use-toast';
 import { Textarea } from '@/components/ui/textarea';
-import { useI18n } from '@/locales/client';
+import { useI18n, useCurrentLocale, useChangeLocale } from '@/locales/client';
+import { Select, SelectContent, SelectItem, SelectTrigger, SelectValue } from '@/components/ui/select';
 
 const mockUserProfile = {
   name: 'Alice Wonderland',
@@ -23,6 +24,8 @@ const mockUserProfile = {
 export default function ProfilePage() {
   const { toast } = useToast();
   const t = useI18n();
+  const currentLocale = useCurrentLocale();
+  const changeLocale = useChangeLocale();
 
   const [name, setName] = useState(mockUserProfile.name);
   const [email, setEmail] = useState(mockUserProfile.email); 
@@ -34,38 +37,57 @@ export default function ProfilePage() {
   const [newPassword, setNewPassword] = useState('');
   const [confirmNewPassword, setConfirmNewPassword] = useState('');
   
+  const [selectedLanguage, setSelectedLanguage] = useState(currentLocale);
+
   const [isLoading, setIsLoading] = useState(false);
   const [isPasswordLoading, setIsPasswordLoading] = useState(false);
+  const [isLanguageLoading, setIsLanguageLoading] = useState(false);
+
+  useEffect(() => {
+    setSelectedLanguage(currentLocale);
+  }, [currentLocale]);
 
   const handleProfileUpdate = async (e: React.FormEvent<HTMLFormElement>) => {
     e.preventDefault();
     setIsLoading(true);
     await new Promise(resolve => setTimeout(resolve, 1000));
     console.log("Updating profile:", { name, avatarUrl, bio, phone, location });
-    toast({ title: "Profile Updated", description: "Your profile information has been saved." }); // Translate
+    toast({ title: t('dashboard.profile.save_button'), description: "Your profile information has been saved." }); 
     setIsLoading(false);
   };
 
   const handlePasswordChange = async (e: React.FormEvent<HTMLFormElement>) => {
     e.preventDefault();
     if (newPassword !== confirmNewPassword) {
-      toast({ title: "Password Mismatch", description: "New passwords do not match.", variant: "destructive" }); // Translate
+      toast({ title: "Password Mismatch", description: "New passwords do not match.", variant: "destructive" }); 
       return;
     }
     if (newPassword.length < 6) {
-      toast({ title: "Password Too Short", description: "Password must be at least 6 characters.", variant: "destructive" }); // Translate
+      toast({ title: "Password Too Short", description: "Password must be at least 6 characters.", variant: "destructive" }); 
       return;
     }
     setIsPasswordLoading(true);
     await new Promise(resolve => setTimeout(resolve, 1000));
     console.log("Changing password");
-    toast({ title: "Password Updated", description: "Your password has been changed successfully." }); // Translate
+    toast({ title: t('dashboard.profile.update_password_button'), description: "Your password has been changed successfully." }); 
     setCurrentPassword('');
     setNewPassword('');
     setConfirmNewPassword('');
     setIsPasswordLoading(false);
   };
 
+  const handleLanguageChange = (newLang: 'en' | 'zh-TW') => {
+    setIsLanguageLoading(true);
+    changeLocale(newLang);
+    localStorage.setItem('userPreferredLanguage', newLang);
+    setSelectedLanguage(newLang);
+    toast({ title: t('dashboard.profile.language_settings_title'), description: t('dashboard.profile.language_updated_toast') });
+    // No need to manually set isLanguageLoading to false if the page reloads/re-renders due to locale change
+    // However, if changeLocale doesn't cause an immediate unmount, manage loading state appropriately.
+    // For simplicity, we assume changeLocale will lead to a re-render where currentLocale updates.
+  };
+
+
   return (
     <div className="space-y-8 max-w-3xl mx-auto">
       <div>
@@ -155,6 +177,32 @@ export default function ProfilePage() {
           </CardFooter>
         </form>
       </Card>
+
+      <Card className="shadow-lg">
+        <CardHeader>
+          <CardTitle className="text-xl font-headline">{t('dashboard.profile.language_settings_title')}</CardTitle>
+          <CardDescription>{t('dashboard.profile.language_settings_description')}</CardDescription>
+        </CardHeader>
+        <CardContent>
+          <div className="space-y-2">
+            <Label htmlFor="language-select">{t('dashboard.profile.display_language_label')}</Label>
+            <Select
+              value={selectedLanguage}
+              onValueChange={(value) => handleLanguageChange(value as 'en' | 'zh-TW')}
+              disabled={isLanguageLoading}
+            >
+              <SelectTrigger id="language-select">
+                <SelectValue placeholder={t('lang.select_language')} />
+              </SelectTrigger>
+              <SelectContent>
+                <SelectItem value="en">{t('lang.english')}</SelectItem>
+                <SelectItem value="zh-TW">{t('lang.traditional_chinese')}</SelectItem>
+              </SelectContent>
+            </Select>
+          </div>
+        </CardContent>
+      </Card>
+
     </div>
   );
 }

src/components/layout/Header.tsx

@@ -15,23 +15,41 @@ import {
 import { useState, useEffect } from 'react';
 import { ThemeToggleButton } from '@/components/ui/theme-toggle';
 import LanguageSwitcher from './LanguageSwitcher';
-import { useI18n, useCurrentLocale } from '@/locales/client';
+import { useI18n, useCurrentLocale, useChangeLocale } from '@/locales/client';
 
 export default function Header() {
   const pathname = usePathname();
   const t = useI18n();
   const locale = useCurrentLocale();
+  const changeLocale = useChangeLocale();
   const [isAuthenticated, setIsAuthenticated] = useState(false);
+  const [isMounted, setIsMounted] = useState(false);
   
   useEffect(() => {
+    setIsMounted(true);
     const authStatus = localStorage.getItem('isToyShareAuthenticated');
     setIsAuthenticated(authStatus === 'true');
-  }, [pathname]); // Listen to pathname changes to re-check auth if needed after navigation
+  }, []); // Run only once on mount
+
+  useEffect(() => {
+    if (isMounted) { // Ensure this runs only on the client after mount
+      const preferredLang = localStorage.getItem('userPreferredLanguage') as 'en' | 'zh-TW' | null;
+      if (preferredLang && preferredLang !== locale) {
+        // Check if the current pathname without locale prefix exists for the preferredLang
+        // This avoids redirect loops if a page doesn't exist in the preferredLang
+        const currentPathWithoutLocale = pathname.startsWith(`/${locale}`) ? pathname.substring(`/${locale}`.length) : pathname;
+        // It's hard to verify if `currentPathWithoutLocale` is valid for `preferredLang` without a full route list
+        // For simplicity, we'll directly change locale. If a 404 occurs, user can switch back.
+        changeLocale(preferredLang);
+      }
+    }
+  }, [isMounted, locale, pathname, changeLocale]);
+
 
   const handleLogout = () => {
     localStorage.removeItem('isToyShareAuthenticated');
     setIsAuthenticated(false);
-    // No need to router.push here, links will use current locale
+    // No need to router.push here, links will use current locale, or redirect logic will apply
   };
 
   // Helper to remove locale prefix for path comparison
@@ -78,7 +96,7 @@ export default function Header() {
                   </DropdownMenuItem>
                   <DropdownMenuSeparator />
                   <DropdownMenuItem onClick={handleLogout}>
-                    <LogIn className="mr-2 h-4 w-4" /> {/* Using LogIn icon for logout action for consistency */}
+                    <LogIn className="mr-2 h-4 w-4" /> 
                     {t('header.logout')}
                   </DropdownMenuItem>
                 </DropdownMenuContent>
@@ -102,7 +120,6 @@ export default function Header() {
           </nav>
           <LanguageSwitcher />
           <ThemeToggleButton />
-           {/* Mobile menu trigger could be added here if needed */}
         </div>
       </div>
     </header>

src/locales/en.ts

@@ -92,8 +92,12 @@ export default {
   'dashboard.profile.confirm_new_password_label': 'Confirm New Password',
   'dashboard.profile.update_password_button': 'Update Password',
   'dashboard.profile.updating_password_button': 'Updating Password...',
+  'dashboard.profile.language_settings_title': 'Language Settings',
+  'dashboard.profile.language_settings_description': 'Choose your preferred display language for the application.',
+  'dashboard.profile.display_language_label': 'Display Language',
+  'dashboard.profile.language_updated_toast': 'Language updated successfully.',
   'lang.english': 'English',
-  'lang.traditional_chinese': '繁體中文',
+  'lang.traditional_chinese': 'Traditional Chinese',
   'lang.select_language': 'Select Language',
   'general.back_to_my_toys': 'Back to My Toys',
   'general.toy_not_found': 'Toy Not Found',

src/locales/zh-TW.ts

@@ -92,6 +92,10 @@ export default {
   'dashboard.profile.confirm_new_password_label': '確認新密碼',
   'dashboard.profile.update_password_button': '更新密碼',
   'dashboard.profile.updating_password_button': '更新密碼中...',
+  'dashboard.profile.language_settings_title': '語言設定',
+  'dashboard.profile.language_settings_description': '選擇您偏好的應用程式顯示語言。',
+  'dashboard.profile.display_language_label': '顯示語言',
+  'dashboard.profile.language_updated_toast': '語言已成功更新。',
   'lang.english': 'English',
   'lang.traditional_chinese': '繁體中文',
   'lang.select_language': '選擇語言',

src/middleware.ts

@@ -3,9 +3,8 @@ import { createI18nMiddleware } from 'next-international/middleware';
 
 const I18nMiddleware = createI18nMiddleware({
   locales: ['en', 'zh-TW'],
-  defaultLocale: 'en',
-  urlMappingStrategy: 'rewrite', // Or 'redirect', depending on preference
-  // prefix: 'as-needed' // default is 'as-needed'
+  defaultLocale: 'zh-TW', // Changed default locale
+  urlMappingStrategy: 'rewrite', 
 });
 
 export function middleware(request: NextRequest) {
@@ -13,6 +12,5 @@ export function middleware(request: NextRequest) {
 }
 
 export const config = {
-  // Matcher ignoring `/_next/` and `/api/`
   matcher: ['/((?!api|_next/static|_next/image|favicon.ico).*)'],
 };