Program.cs

using Microsoft.AspNetCore.Localization;
using Microsoft.AspNetCore.Localization.Routing;
using Microsoft.Extensions.Options;
using System.Globalization;

var builder = WebApplication.CreateBuilder(args);

// Add localization services before AddControllersWithViews.
builder.Services.AddLocalization(options => options.ResourcesPath = "Resources");

builder.Services.Configure<RequestLocalizationOptions>(options =>
{
    var supportedCultures = new List<CultureInfo>
    {
        new CultureInfo("tr-TR"),
        new CultureInfo("en-US")
    };

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

    // Route üzerinden culture alımı için
    var routeProvider = new RouteDataRequestCultureProvider
    {
        Options = options
    };

    options.RequestCultureProviders.Insert(0, routeProvider);
});

// Add services to the container.
builder.Services.AddControllersWithViews()
    .AddViewLocalization()
    .AddDataAnnotationsLocalization();

var app = builder.Build();

// Configure the HTTP request pipeline.
if (!app.Environment.IsDevelopment())
{
    app.UseExceptionHandler("/Home/Error");
}

app.UseRouting();

app.UseAuthorization();

app.MapStaticAssets();

var localizationOptions = app.Services.GetRequiredService<IOptions<RequestLocalizationOptions>>().Value;
app.UseRequestLocalization(localizationOptions);

app.MapControllerRoute(
    name: "default",
     pattern: "{culture=en-US}/{controller=Home}/{action=Index}/{id?}")
    .WithStaticAssets();


app.Run();