ASP.NET Core Razor Pages：如何设置非en-US的请求本地化默认区域性

问题概述 #

使用VS2022的“ASP.NET Core Web App (Razor Pages)”模板创建了目标框架为.NET 8.0的Web应用WebApplication2，目前遇到本地化配置冲突：仅能二选一——要么通过URL参数（如?culture=fr-FR）切换请求本地化，要么将应用默认语言固定为fr-FR，无法同时实现两者。两种场景下本地化翻译功能均正常，但无法兼顾默认语言设置与URL参数切换。

情况1：URL参数生效，但默认语言无法设为fr-FR #

尽管在配置中指定默认区域性为fr-FR，应用启动后仍默认使用en-US，对应Program.cs代码如下：

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.
builder.Services.AddControllersWithViews();
// Add localization services
builder.Services.AddLocalization(options => options.ResourcesPath = "Resources");


string[] supportedCultures = [ "fr-FR", "en-US", "es-ES" ];
builder.Services.Configure<RequestLocalizationOptions>(options =>
{
    options.DefaultRequestCulture = new RequestCulture("fr-FR");
    options.SetDefaultCulture("fr-FR")
           .AddSupportedCultures(supportedCultures)
           .AddSupportedUICultures(supportedCultures);
});

var app = builder.Build();

// Configure the HTTP request pipeline.
if (!app.Environment.IsDevelopment())
{
    app.UseExceptionHandler("/Home/Error");
    // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
    app.UseHsts();
}

var localizationOptions = app.Services.GetService<IOptions<RequestLocalizationOptions>>()?.Value;
if (localizationOptions != null)
{
    localizationOptions.AddSupportedCultures(supportedCultures);
    localizationOptions.DefaultRequestCulture = new RequestCulture("fr-FR");
    app.UseRequestLocalization(localizationOptions);
}

app.UseHttpsRedirection();
app.UseStaticFiles();

app.UseRouting();

app.UseAuthorization();

app.MapControllerRoute(
    name: "default",
    pattern: "{controller=Home}/{action=Index}/{id?}");

app.Run();

情况2：默认语言设为fr-FR，但URL参数切换失效 #

将区域性固定为fr-FR后，?culture=en-US这类URL参数不再生效，修改后的代码片段如下：

/* Comment these lines and replace it with single app.UseRequestLocalization call */
// var localizationOptions = app.Services.GetService<IOptions<RequestLocalizationOptions>>()?.Value;
// if (localizationOptions != null)
// {
//     localizationOptions.AddSupportedCultures(supportedCultures);
//     localizationOptions.DefaultRequestCulture = new RequestCulture("fr-FR");
//     app.UseRequestLocalization(localizationOptions);
// }
/* This has effect but then URL like `?culture=en-US` doesn't work */
app.UseRequestLocalization("fr-FR");

项目配置细节 #

• 项目根目录下有Resources文件夹，包含3个资源文件（各含字符串StrLearnAbout）：
  • Resources/SharedResource.en-US.resx
  • Resources/SharedResource.es-ES.resx
  • Resources/SharedResource.fr-FR.resx
• 根目录下有空类SharedResource：

namespace WebApplication2
{
    public class SharedResource
    {
    }
}

• Index.cshtml代码：

@using Microsoft.Extensions.Localization
@inject IStringLocalizer<SharedResource> Localizer

@{
    ViewData["Title"] = "Home Page";
}

<div class="text-center">
    <h1 class="display-4">Welcome</h1>
    <p>@Localizer["StrLearnAbout"]</p>
    <p>Learn about <a href="https://learn.microsoft.com/aspnet/core">building Web apps with ASP.NET Core</a>.</p>
</div>

解决方案 #

问题核心在于请求本地化中间件的配置顺序与重复配置冲突，修改后可同时满足默认语言设置与URL参数切换需求：

修改后的Program.cs #

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.
builder.Services.AddControllersWithViews();
// Add localization services
builder.Services.AddLocalization(options => options.ResourcesPath = "Resources");

string[] supportedCultures = [ "fr-FR", "en-US", "es-ES" ];
builder.Services.Configure<RequestLocalizationOptions>(options =>
{
    // 设置默认区域性
    var defaultCulture = "fr-FR";
    options.DefaultRequestCulture = new RequestCulture(defaultCulture);
    options.SetDefaultCulture(defaultCulture)
           .AddSupportedCultures(supportedCultures)
           .AddSupportedUICultures(supportedCultures);

    // 确保URL参数提供器优先级最高（默认已启用，显式声明更稳妥）
    options.RequestCultureProviders.Insert(0, new QueryStringRequestCultureProvider());
});

var app = builder.Build();

// Configure the HTTP request pipeline.
if (!app.Environment.IsDevelopment())
{
    app.UseExceptionHandler("/Home/Error");
    app.UseHsts();
}

// 关键：在UseRouting之前启用请求本地化中间件
app.UseRequestLocalization();

app.UseHttpsRedirection();
app.UseStaticFiles();

app.UseRouting();

app.UseAuthorization();

app.MapControllerRoute(
    name: "default",
    pattern: "{controller=Home}/{action=Index}/{id?}");

app.Run();

关键说明 #

1. 中间件顺序：UseRequestLocalization必须放在UseRouting之前，否则路由匹配会先于本地化处理，导致URL参数无法生效。
2. 避免重复配置：移除服务构建后对RequestLocalizationOptions的二次修改，服务配置阶段的设置已足够，重复修改会干扰默认逻辑。
3. URL参数优先级：显式将QueryStringRequestCultureProvider插入到提供器列表首位，确保URL参数的优先级高于Cookie、Accept-Language头等其他本地化来源。

配置完成后，应用默认将使用fr-FR，同时访问?culture=en-US或?culture=es-ES时，会正常切换到对应语言。

内容的提问来源于stack exchange，提问作者char m