Asp.Net MVC localizing routes with default language - asp.net-mvc

Question

I need to provide language specific routes for my Asp.Net MVC application. The language should be part of the Url Path (http://myapp/en/Blog) and when it is ommitted the default language have to be used.
http://myapp/en/Blog -> Blog in the English version
http://myapp/Blog -> Blog in the Default (portuguese) Language version
To address this issue I created two Routes bellow:
routes.MapRoute(
name: "Default.lang",
url: "{lang}/{controller}/{action}/{id}",
defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional },
constraints: new { lang = #"^[a-zA-Z]{2}$" }
);
routes.MapRoute(
name: "Default",
url: "{controller}/{action}/{id}",
defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }
);
The routes are working as expected but I'm getting weird results when I try to use the Url.RouteUrl method to get alternative language urls.
Example 1 - Path: /
url.Action("Index", "Blog") // returns "/Blog" that is OK
url.Action("Index", "Blog", new { lang = "en" }); // returns "/en/Blog" that is also OK
Example 2 - Path: /en
url.Action("Index", "Home") // returns "/en/Blog" (??????????) Not OK
url.Action("Index", "Home", new { lang = "en" }); // returns "/en/Blog" that is OK
As you can see I get a wrong result when I access the url http://myappurl/en and try to use the Url.Action method without pass any route value (same result with Url.RouteUrl)
Does anyone knows what is wrong with my routes?
[EDIT] I'm not sure if the issue is related to the route because I've tested the routes using "en" as first route's constraint and I got the same result.

Answer 1

After some digging inside System.Web.Mvc and System.Web.Routing source code I found that this behavior is expected. I presume that it is designed to correctly work in applications running inside Virtual Directories.
This can be confirmed in this answer that I found when was researching if someone else had the same problem with virtual path and route resolution.
Workaround
Use named route resolution with Url.RouteUrl method that has and different implementation and works as expected.
Example:
var blogDefaultUrl = url.RouteUrl("Default", new {action = "Index", controller = "Blog"});
var blogLangageSpecifictUrl = url.RouteUrl("Default.lang", new { action = "Index", controller = "Blog", lang = language });
I was avoiding to use named routes because my application design is a little bit more complicated than I demonstrated above. By this reason I have to discover at run time the route that matches the Request.Url and from that point I call the RouteUrl to get the alternative languages url to the content.