feat: Implement client-side localization using JSON files, a custom localizer, and a new language switcher component.

apps/web-client-base-net/src/WebClientBase.Server/Program.cs

@@ -3,6 +3,8 @@
 /// VI: ASP.NET Core BFF (Backend for Frontend) với YARP Reverse Proxy.
 /// </summary>
 
+using Microsoft.AspNetCore.Rewrite;
+
 var builder = WebApplication.CreateBuilder(args);
 
 // ═══════════════════════════════════════════════════════════════════════════════
@@ -54,10 +56,18 @@ if (app.Environment.IsDevelopment())
 
 app.UseHttpsRedirection();
 
+// EN: Enable CORS
+// VI: Kích hoạt CORS
 // EN: Enable CORS
 // VI: Kích hoạt CORS
 app.UseCors("BlazorClient");
 
+// EN: Rewrite localized framework/content requests to root
+// VI: Viết lại các yêu cầu framework/content từ đường dẫn ngôn ngữ về root
+var rewriteOptions = new RewriteOptions()
+    .AddRewrite(@"^(en-US|vi-VN)/(_framework|_content)/(.*)", "$2/$3", skipRemainingRules: true);
+app.UseRewriter(rewriteOptions);
+
 // EN: Serve static files with fingerprinting support (.NET 10+)
 // VI: Phục vụ static files với hỗ trợ fingerprinting (.NET 10+)
 app.MapStaticAssets();
@@ -70,8 +80,44 @@ app.MapHealthChecks("/health");
 // VI: Map các routes YARP Reverse Proxy đến microservices
 app.MapReverseProxy();
 
-// EN: Fallback to index.html for SPA routing
-// VI: Fallback đến index.html cho SPA routing
+// EN: Localization Support - Serve index.html with dynamic base tag for specific cultures
+// VI: Hỗ trợ đa ngôn ngữ - Phục vụ index.html với base tag động cho các ngôn ngữ cụ thể
+var supportedCultures = new[] { "en-US", "vi-VN" };
+var localizationOptions = new RequestLocalizationOptions()
+    .SetDefaultCulture("en-US")
+    .AddSupportedCultures(supportedCultures)
+    .AddSupportedUICultures(supportedCultures);
+
+app.UseRequestLocalization(localizationOptions);
+
+// Handle mapped culture routes (e.g. /en-US/home, /vi-VN/solutions)
+app.Map("{culture:regex(^(en-US|vi-VN)$)}/{**slug}", async (string culture, HttpContext context, IWebHostEnvironment env) => 
+{
+    // Try to find index.html
+    var fileInfo = env.WebRootFileProvider.GetFileInfo("index.html");
+    if (!fileInfo.Exists)
+    {
+        // In Development with Hosted Blazor, index.html might not be in Server's wwwroot strictly directly depending on setup,
+        // but typically it is served via StaticFiles/BlazorFrameworkFiles.
+        // If we can't find it easily via IWebHostEnvironment in Dev, we might fail.
+        // However, for this task let's assume standard structure or handle gracefully.
+        return Results.NotFound("index.html not found in wwwroot. Ensure the Client project is built.");
+    }
+
+    using var stream = fileInfo.CreateReadStream();
+    using var reader = new StreamReader(stream);
+    var html = await reader.ReadToEndAsync();
+    
+    // Replace base tag: <base href="/" /> -> <base href="/vi-VN/" />
+    // Be robust with spaces or standard format
+    var modifiedHtml = html.Replace("<base href=\"/\" />", $"<base href=\"/{culture}/\" />")
+                           .Replace("<base href=\"/\"/>", $"<base href=\"/{culture}/\" />");
+
+    return Results.Content(modifiedHtml, "text/html");
+});
+
+// EN: Fallback to index.html for SPA routing (default culture)
+// VI: Fallback đến index.html cho SPA routing (ngôn ngữ mặc định)
 app.MapFallbackToFile("index.html");
 
 app.Run();