builder.Services.Configure<RequestLocalizationOptions>(options => {
    var supportedCultures = new[]
    {
        CultureInfo.InvariantCulture,
        CultureInfo.GetCultureInfo("fr"),
        CultureInfo.GetCultureInfo("en"),
    };

    options.DefaultRequestCulture = new(supportedCultures[1]);
    options.SupportedCultures = supportedCultures;
    options.SupportedUICultures = supportedCultures;

    options.RequestCultureProviders =
    [
        new DefaultRequestCultureProvider()
    ];
});

public class DefaultRequestCultureProvider : IRequestCultureProvider
{
    public Task<ProviderCultureResult?> DetermineProviderCultureResult(HttpContext httpContext)
    {
        var result = new ProviderCultureResult(culture: CultureInfo.InvariantCulture.Name, uiCulture: CultureInfo.CurrentUICulture.Name);

        return Task.FromResult<ProviderCultureResult?>(result);
    }
}