public class RouteValueRequestCultureProvider : RequestCultureProvider
{
  public override Task DetermineProviderCultureResult(HttpContext httpContext)
  {
    string cultureCode = null;

    if (httpContext.Request.Path.HasValue && httpContext.Request.Path.Value == "/")
      cultureCode = this.GetDefaultCultureCode();

    // TODO: make it look more beautiful
    else if (httpContext.Request.Path.HasValue && httpContext.Request.Path.Value.Length >= 4 && httpContext.Request.Path.Value[0] == '/' && httpContext.Request.Path.Value[3] == '/')
    {
      cultureCode = httpContext.Request.Path.Value.Substring(1, 2);

      if (!this.CheckCultureCode(cultureCode))
        cultureCode = this.GetDefaultCultureCode(); //throw new HttpException(HttpStatusCode.NotFound);
    }

    else cultureCode = this.GetDefaultCultureCode(); //throw new HttpException(HttpStatusCode.NotFound);

    // TODO: from the SEO point of view, we should return 404 error code for unknown cultures

    ProviderCultureResult requestCulture = new ProviderCultureResult(cultureCode);

    return Task.FromResult(requestCulture);
  }

  private string GetDefaultCultureCode()
  {
    return this.Options.DefaultRequestCulture.Culture.TwoLetterISOLanguageName;
  }

  private bool CheckCultureCode(string cultureCode)
  {
    return this.Options.SupportedCultures.Select(c => c.TwoLetterISOLanguageName).Contains(cultureCode);
  }
}

این کد زبان  درون url چک می کند. اگر درون url زبان یافت نشد زبانی که به عنوان زبان پیش فرض ست شده است را استفاده می کند.

سپس ما به برنامه وبی خود می گوییم که از request localization middleware  به عنوان یک انتخاب استفاده کند:

public void Configure(IApplicationBuilder applicationBuilder)
{
  RequestLocalizationOptions requestLocalizationOptions = new RequestLocalizationOptions();

  requestLocalizationOptions.SupportedCultures = requestLocalizationOptions.SupportedUICultures =
    new CultureInfo[] { new CultureInfo("en"), new CultureInfo("ru"), new CultureInfo("uk") }.ToList();

  requestLocalizationOptions.RequestCultureProviders.Insert(0, new RouteValueRequestCultureProvider() { Options = requestLocalizationOptions });
  applicationBuilder.UseRequestLocalization(requestLocalizationOptions);
  applicationBuilder.UseMvc(configureRoutes =>
    {
      configureRoutes.MapRoute(name: "Default", template: "{culture}/{controller}/{action}/{id?}", defaults: new { culture = "en", controller = "Default", action = "Index" });
    }
  );
}