Seo – "culture" query string is not migrated

public void ConfigureServices(IServiceCollection services)
{
    services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();

    services.AddLocalization();

    services.AddMvc(option => option.EnableEndpointRouting = false);

    services.Configure<RequestLocalizationOptions>(options =>
    {
        var supportedCultures = new[]
                 {
                     new CultureInfo("en-US"),
                     new CultureInfo("tr-TR")
                 };

        options.DefaultRequestCulture = new RequestCulture(culture: "en-US", uiCulture: "en-US");
        options.SupportedCultures = supportedCultures;
        options.SupportedUICultures = supportedCultures;
        options.RequestCultureProviders = new[] { new RouteDataRequestCultureProvider {
            IndexOfCulture = 1,
            IndexofUICulture = 1
        }};
    });

    services.Configure<RouteOptions>(options =>
    {
        options.ConstraintMap.Add("culture", typeof(LanguageRouteConstraint));
    });
}

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    if (env.IsDevelopment())
    {
        app.UseDeveloperExceptionPage();
    } 

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

    app.UseHttpsRedirection();

    //SEO - jpg, css, js gibi dosyalara cache eklemek için
    app.UseStaticFiles(new StaticFileOptions
    {
        OnPrepareResponse = ctx =>
        {
            const int durationInSeconds = 60 * 60 * 24 * 365;
            ctx.Context.Response.Headers[Microsoft.Net.Http.Headers.HeaderNames.CacheControl]
            = "public,max-age=" + durationInSeconds;
        }
    });

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

        routes.MapRoute(
                name: "DefaultNonLocalized",
                template: "{controller}/{action}/{id?}"
        );

        routes.MapRoute(
              name: "default",
              template: "",
              defaults: new { controller = "Home", action = "RedirectToDefaultLanguage", culture = "tr" });

        routes.MapRoute(
             name: "error",
             template: "{*catchall}",
             defaults: new { controller = "Error", action = "HandleError", statusCode = 404 });
    });
}

public class LanguageRouteConstraint : IRouteConstraint
{
    public bool Match(HttpContext httpContext, IRouter route, string routeKey, RouteValueDictionary values, RouteDirection routeDirection)
    {
        if (!values.ContainsKey("culture"))
            return false;

        var culture = values["culture"].ToString();
        return culture == "en" || culture == "tr";
    }
}

public class RouteDataRequestCultureProvider : RequestCultureProvider
{
    public int IndexOfCulture;
    public int IndexofUICulture;

    public override Task<ProviderCultureResult> DetermineProviderCultureResult(HttpContext httpContext)
    {
        if (httpContext == null)
            throw new ArgumentNullException(nameof(httpContext));

        string culture = null;
        string uiCulture = null;

        var twoLetterCultureName = httpContext.Request.Path.Value.Split('/')[IndexOfCulture]?.ToString();
        var twoLetterUICultureName = httpContext.Request.Path.Value.Split('/')[IndexofUICulture]?.ToString();

        if (twoLetterCultureName == "tr")
            culture = "tr-TR";
        else if (twoLetterCultureName == "en")
            culture = "en-US";
         
        if (twoLetterUICultureName == "tr")
            uiCulture = "tr-TR";
        else if (twoLetterUICultureName == "en")
            uiCulture = "en-US";
       
        if (culture == null && uiCulture == null)
            return NullProviderCultureResult;

        if (culture != null && uiCulture == null)
            uiCulture = culture;

        if (culture == null && uiCulture != null)
            culture = uiCulture;

        var providerResultCulture = new ProviderCultureResult(culture, uiCulture);

        return Task.FromResult(providerResultCulture);
    }
}

public ActionResult RedirectToDefaultLanguage()
{
    return RedirectToAction("Index", new { culture = "en"});
}

[Route("{culture}")]
public IActionResult Index(string culture)
{
    MainViewModel model = new MainViewModel();

    ProductListViewModel m1 = new ProductListViewModel();
    ProductListViewModel m2 = new ProductListViewModel();

    if (culture == "tr")
    {
        m1.Id = 1;
        m1.Name = "ürün 1 tr";
        m1.SeoUrl = "urun-tr";

        m2.Id = 2;
        m2.Name = "ürün 2 tr";
        m2.SeoUrl = "urun-tr";
    }
    else
    {
        m1.Id = 1;
        m1.Name = "product 1 en";
        m1.SeoUrl = "product-en";

        m2.Id = 2;
        m2.Name = "product 2 en";
        m2.SeoUrl = "product-en";
    }

    model.Products.Add(m1);
    model.Products.Add(m2);

    return View(model);
}

[Route("{culture}/{seoTag:regex(egitim|training)}/{productUrl}-{productId:int}-{seoTag2:regex([[egitimi$|training$]])}/", Name = "productLink")]
public ActionResult ProductDetails(string culture, int productId, string productUrl)
{
    return View();
}

//IN VIEW
//Everything works
@foreach (var item in Model.Products)
{
    <div>
        <a asp-route="productLink" asp-route-productId="@item.Id" asp-route-productUrl="@item.SeoUrl" asp-route-seoTag="@SharedLocalizer["TrainingSeoTag"]" asp-route-seoTag2="@SharedLocalizer["ProductSeoUrl"]">
            @item.Name
        </a>
    </div>
    <hr />
}

There is no asp-route-culture="*culture-code*", but "culture" is still carried when linking to the other page.

When you do this project with ASP.NET Core 6 MVC, the "culture" query string is not moved to the other page. I need to add parameter with asp-route-culture="*code".

This is the ASP.NET Core 6 MVC code:

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.
builder.Services.AddControllersWithViews(option => option.EnableEndpointRouting = false);
builder.Services.AddHttpContextAccessor();
builder.Services.AddLocalization();
 
builder.Services.Configure<RequestLocalizationOptions>(options =>
{
    var supportedCultures = new[]
              {
                  new CultureInfo("en-US"),
                  new CultureInfo("tr-TR"),
                  new CultureInfo("es-US")
              };

    options.DefaultRequestCulture = new RequestCulture(culture: "tr-TR", uiCulture: "tr-TR");
    options.SupportedCultures = supportedCultures;
    options.SupportedUICultures = supportedCultures;
    options.RequestCultureProviders = new[] { new Custom2RequestCultureProvider {
                    IndexOfCulture = 1,
                    IndexofUICulture = 1
                }
};
});

builder.Services.Configure<RouteOptions>(options =>
{
    options.ConstraintMap.Add("culture", typeof(LanguageRouteConstraint));
});

var app = builder.Build();

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

if (!app.Environment.IsDevelopment())
{
    app.UseExceptionHandler("/Home/Error");
    app.UseHsts();
}

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

app.UseRouting();

app.MapControllerRoute(
            name: "LocalizedDefault",
            pattern: "{culture:culture}/{controller=Home}/{action=Index}/{id?}"
    );

app.MapControllerRoute(
            name: "DefaultNonLocalized",
            pattern: "{controller}/{action}/{id?}"
    );

app.MapControllerRoute(
          name: "default",
          pattern: "",
          defaults: new { controller = "Home", action = "RedirectToDefaultLanguage", culture = "tr-TR" });

app.MapControllerRoute(
         name: "error",
         pattern: "{*catchall}",
         defaults: new { controller = "Error", action = "HandleError", statusCode = 404 });
 
app.Run();

//***
//IN VIEW
//If I don't add asp-route-culture="en" it doesn't work
//***
<a asp-route="productLink" asp-route-productId="@item.Id" asp-route-productUrl="@item.SeoUrl" asp-route-seoTag="@SharedLocalizer["TrainingSeoTag"]" asp-route-seoTag2="@SharedLocalizer["ProductSeoUrl"]">
    @item.Name
</a>

QUESTION: Why is asp-route-culture="" not required in ASP.NET MVC 3, but required in ASP.NET Core 6 MVC ?

My ASP.NET MVC 3 project files : https://filetransfer.io/data-package/ljsHJom3#link

My ASP.NET Core 6 MVC project files: https://filetransfer.io/data-package/Go4VK5FB#link