Convert-it/Program.cs

using System.Globalization;
using Microsoft.AspNetCore.Localization;
using Microsoft.AspNetCore.Localization.Routing;
using Microsoft.Extensions.Options;
using Convert_It_Online.Services;
using Convert_It_Online.Middleware;

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddLocalization();

builder.Services.AddSingleton<IUrlTranslationService, UrlTranslationService>();

var supportedCultures = new[] { "pt-BR", "es-MX", "es-CL", "es-PY" };
builder.Services.Configure<RequestLocalizationOptions>(options =>
{
    options.DefaultRequestCulture = new RequestCulture("pt-BR");
    options.SupportedCultures = supportedCultures.Select(c => new CultureInfo(c)).ToList();
    options.SupportedUICultures = supportedCultures.Select(c => new CultureInfo(c)).ToList();
});

builder.Services.AddControllersWithViews()
    .AddViewLocalization(Microsoft.AspNetCore.Mvc.Razor.LanguageViewLocationExpanderFormat.Suffix);

var app = builder.Build();

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

localizationOptions.RequestCultureProviders.Clear();
localizationOptions.RequestCultureProviders.Insert(0, new RouteDataRequestCultureProvider());
localizationOptions.RequestCultureProviders.Insert(1, new AcceptLanguageHeaderRequestCultureProvider());
localizationOptions.RequestCultureProviders.Insert(2, new QueryStringRequestCultureProvider());

// 3. Pipeline de Middlewares (na ordem correta)
if (app.Environment.IsDevelopment())
{
    app.UseDeveloperExceptionPage();
}

app.UseExceptionHandler("/Home/Error");
app.UseHsts();

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

app.UseMiddleware<UrlTranslationMiddleware>();
app.UseRouting();
app.UseRequestLocalization(localizationOptions);
app.UseAuthorization();

app.MapControllerRoute(
    name: "areaRoute",
    pattern: "{culture:length(2,5)}/{area:exists}/{controller=Home}/{action=Index}/{id?}");

app.MapControllerRoute(
    name: "default",
    pattern: "{culture:length(2,5)}/{controller=Home}/{action=Index}/{id?}");

app.MapControllerRoute(
    name: "root",
    pattern: "{controller=Home}/{action=Index}/{id?}",
    defaults: new { culture = "pt-BR" });

app.Run();