Startup.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Identity;
using Microsoft.AspNetCore.Identity.UI;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.HttpsPolicy;
using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;
using AspNetCoreIdentityLocalization.Data;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using System.Globalization;
using Microsoft.AspNetCore.Localization;
using Microsoft.Extensions.Options;
using AspNetCoreIdentityLocalization.Resources;
using AspNetCoreIdentityLocalization.Services;

namespace AspNetCoreIdentityLocalization
{
    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            services.Configure<CookiePolicyOptions>(options =>
            {
                // This lambda determines whether user consent for non-essential cookies is needed for a given request.
                options.CheckConsentNeeded = context => true;
                options.MinimumSameSitePolicy = SameSiteMode.None;
            });

            services.AddDbContext<ApplicationDbContext>(options =>
                options.UseSqlServer(
                    Configuration.GetConnectionString("DefaultConnection")));
            services.AddDefaultIdentity<IdentityUser>()
                //.AddDefaultUI(UIFramework.Bootstrap4)
                .AddErrorDescriber<LocalizedIdentityErrorDescriber>()
                .AddEntityFrameworkStores<ApplicationDbContext>();

            services.AddLocalization(options => options.ResourcesPath = "Resources");

            services.AddMvc(options =>
                {
                    options.SetConventionalMetadataProviders<Resources.DisplayMetadataSharedResource , Resources.ValidationMetadataSharedResource>();
                })
                .SetCompatibilityVersion(CompatibilityVersion.Version_2_2)
                .AddViewLocalization()
                .AddDataAnnotationsLocalization(options =>
                {
                    options.DataAnnotationLocalizerProvider = (type, factory) =>
                        factory.Create(typeof(DataAnnotationSharedResource));
                });

            services.Configure<RequestLocalizationOptions>(options =>
            {
                var supportedCultures = new List<CultureInfo>
                    {
                        new CultureInfo("en"),
                        new CultureInfo("zh-TW"),
                        new CultureInfo("zu-ZA"), //for fall back testing
                    };

                options.DefaultRequestCulture = new RequestCulture("en");
                options.SupportedCultures = supportedCultures;
                options.SupportedUICultures = supportedCultures;
            });
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
                app.UseDatabaseErrorPage();
            }
            else
            {
                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();
            }

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

            app.UseAuthentication();

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

            app.UseMvc(routes =>
            {
                routes.MapRoute(
                    name: "default",
                    template: "{controller=Home}/{action=Index}/{id?}");
            });
        }
    }
}