Alternate Startup pattern for option settings. Especially useful when the settings rely on services.

Startup.cs

using System.Globalization;
using System.Reflection;
using Localized._1._1_preview.Models;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Razor;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.FileProviders;
using Microsoft.Extensions.Localization;
using Microsoft.Extensions.Logging;

namespace Wrap.Localized
{
    public class Startup
    {
        public Startup(IHostingEnvironment env)
        {
            var builder = new ConfigurationBuilder()
                .SetBasePath(env.ContentRootPath)
                .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
                .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true)
                .AddEnvironmentVariables();
            Configuration = builder.Build();
        }

        public IConfigurationRoot Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            // Embedded provider for views in the class library.
            services
                .AddMvc()
                .AddDataAnnotationsLocalization()
                .AddViewLocalization();

            // Might execute markers e.g. services.Configure<MvcOptions>() as well.
        }

        public void ConfigureOptions(LocalizationOptions options)
        {
            options.ResourcesPath = "Resources";
        }

        public void ConfigureOptions(MvcOptions options, IStringLocalizer<Model> localizer)
        {
            options.ModelBindingMessageProvider.ValueMustNotBeNullAccessor =
                    value => localizer["Value '{0}' appears to be null and that's not valid.", value];
        }

        public void ConfigureOptions(RazorViewEngineOptions options)
        {
            var embeddedProvider = new EmbeddedFileProvider(typeof(Model).GetTypeInfo().Assembly);

            options.FileProviders.Add(embeddedProvider);
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
        {
            loggerFactory.AddConsole(Configuration.GetSection("Logging"));
            loggerFactory.AddDebug();

            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                app.UseExceptionHandler("/Home/Error");
            }

            var options = new RequestLocalizationOptions();
            foreach (var culture in new[]
            {
                new CultureInfo("de") ,
                new CultureInfo("de-DE"),
                new CultureInfo("fr"),
                new CultureInfo("fr-CA"),
            })
            {
                options.SupportedCultures.Add(culture);
                options.SupportedUICultures.Add(culture);
            }

            app.UseRequestLocalization(options);
            app.UseStaticFiles();
            app.UseMvcWithDefaultRoute();
        }
    }
}