ASP.NET Core WebAPI 實作本地化（單資源檔案）

在 Startup ConfigureServices 註冊在地化所需的服務 AddLocalization 和 Configure<RequestLocalizationOptions>

public void ConfigureServices(IServiceCollection services)
{
    services.AddLocalization();
    services.Configure<RequestLocalizationOptions>(options =>
    {
        var supportedCultures = new List<CultureInfo>
        {
            new CultureInfo("en-us"),
            new CultureInfo("zh-cn")
        };

        options.DefaultRequestCulture = new RequestCulture(culture: "en-us", uiCulture: "en-us");
        options.SupportedCultures = supportedCultures;
        options.SupportedUICultures = supportedCultures;
        options.RequestCultureProviders = new IRequestCultureProvider[] { new RouteDataRequestCultureProvider { IndexOfCulture = 1, IndexofUiCulture = 1 } };
    });
    services.Configure<RouteOptions>(options =>
    {
        options.ConstraintMap.Add("culture", typeof(LanguageRouteConstraint));
    });
    services.AddControllers();
}

在 Startup.cs 類別的 Configure 方法中新增請求在地化中介軟體。

var localizeOptions = app.ApplicationServices.GetService<IOptions<RequestLocalizationOptions>>();
            app.UseRequestLocalization(localizeOptions.Value);

RequestCultureProvider 它使用簡單的委派來決定當前的在地化地區設定，當然我們還可以透過 RequestCultureProvider 自訂來源的請求區域資訊，例如設定檔或資料庫都是可以的。或者說我們可以選用預設的一些方式讓我們去取得當前區域。

ASP.NET Core 在地化預設向我們提供了四個方式，可用於決定正在執行的請求的當前地區設定：

• QueryStringRequestCultureProvider
• CookieRequestCultureProvider
• AcceptLanguageHeaderRequestCultureProvider
• CustomRequestCultureProvider

如下所示我將透過路由的方式，去決定當前區域

public class RouteDataRequestCultureProvider : RequestCultureProvider
{
    public int IndexOfCulture;
    public int IndexofUiCulture;

    public override Task<ProviderCultureResult> DetermineProviderCultureResult(HttpContext httpContext)
    {
        if (httpContext == null)
            throw new ArgumentNullException(nameof(httpContext));
        string uiCulture;

        string culture = uiCulture = httpContext.Request.Path.Value.Split('/')[IndexOfCulture];

        var providerResultCulture = new ProviderCultureResult(culture, uiCulture);

        return Task.FromResult(providerResultCulture);
    }
}

透過如下程式碼片段實現 IRouteConstraint 對路由做相應的約束

public class LanguageRouteConstraint : IRouteConstraint
{
    public bool Match(HttpContext httpContext, IRouter route, string routeKey, RouteValueDictionary values, RouteDirection routeDirection)
    {

        if (!values.ContainsKey("culture"))
            return false;

        var culture = values["culture"].ToString();
        return culture == "en-us" || culture == "zh-cn";
    }
}

新增區域資源檔

[Route("{culture:culture}/[controller]")]
[ApiController]
public class HomeController : ControllerBase
{
    private readonly IStringLocalizer<Resource> localizer;
    public HomeController(IStringLocalizer<Resource> localizer)
    {
        this.localizer = localizer;
    }
    public string Get()
    {
        return localizer["Home"];
    }
}

Reference：https://github.com/hueifeng/BlogSample/tree/master/src/LocalizationSingleResx