Where to put RequestLocalization in the order?

[Ruard]

This issue is about the order of configuration.

string[] SupportedCultures = new[] { "en", "de", "fr", "nl" };

My configuration:

services.AddControllersWithViews()
    .SetCompatibilityVersion(CompatibilityVersion.Version_3_0)
    .AddViewLocalization();

services.AddLocalization();

services.Configure<RequestLocalizationOptions>(options =>
{
    options.AddSupportedCultures(SupportedCultures)
        .AddSupportedUICultures(SupportedCultures)
        .SetDefaultCulture("en");

    options.AddInitialRequestCultureProvider(new RouteDataRequestCultureProvider());
});

The current documentation, which is not up-to-date BTW:

The localization middleware must be configured before any middleware which might check the request culture

app.UseRequestLocalization(new RequestLocalizationOptions { });
app.UseStaticFiles();
app.UseAuthentication();

But RouteDataRequestCultureProvider is ignored when I put UseRequestLocalization before StaticFiles (or actually before UseRouting):

app.UseRequestLocalization(); // <--
app.UseStaticFiles();
app.UseRouting();
app.UseAuthentication();
app.UseAuthorization();

And works only when put after UseRouting:

app.UseStaticFiles();
app.UseRouting();
app.UseRequestLocalization(); // <--
app.UseAuthentication();
app.UseAuthorization();

I don't see how I could use the RouteData for e.g. static files or custom middleware that comes after UseRequestLocalization and before UseRouting. How should this be solved?

Additional information:

var cultureString = string.Join("|", SupportedCultures);

app.UseEndpoints(endpoints =>
{
    endpoints.MapControllerRoute("default", "{culture:regex(^(" + cultureString + ")$)}/{controller=Home}/{action=Index}/{id?}");
    endpoints.MapDefaultControllerRoute();
});

[javiercn]

@Ruard thanks for contacting us.

The routing middleware in endpoint routing only decides what route matches. The request continues to flow through the remaining middlewares and the route data is available after the routing middleware has run.

The right thing to do is to put UseLocalizalization after UseRouting.