Post_12_2.cs

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" });
    }
  );
}