在Startup ConfigureServices 注册本地化所需要的服务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类的Configure 方法中添加请求本地化中间件。

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

RequestCultureProvider 它使用简单的委托来确定当前的本地化区域性，当然我们还可以通过RequestCultureProvider自定义源的请求区域信息比如说配置文件或者数据库都是可以的.或者说我们可以选用默认的一些方式让我们去获取到当前区域.

ASP.NET Core 本地化默认向我们提供了四个方式，可用于确定正在执行的请求的当前区域性：

• QueryStringRequestCultureProvider
• CookieRequestCultureProvider
• AcceptLanguageHeaderRequestCultureProvider
• CustomRequestCultureProvider

如下所示我将通过路由的方式,去确定当前区域

   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);
        }
    }

通过如下代码片段实现IRouteConstraint对路由做相应的约束

    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";
        }
    }

添加区域资源文件

注入IStringLocalizer<T>，StringLocalizer将通过传递的共享资源(T)的值映射到资源文件,然后将本地化根据字符串的名称从资源文件返回响应的值

    [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"];
        }
    }

如下图所示

Reference

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

ASP.NET Core WebAPI实现本地化（单资源文件）