Reconstructing a Razor URL using referring URL and language selection - asp.net-mvc

Question

To implement language selection in an MVC Razor application, I use a leading path segment in the route mapping like www.mydomain.com/lang/controller/action/id?param= where lang is a 2 letter ISO country code like fr, de, it, en etc
I use the following route mapping (which works fine):
// Special localisation route mapping - expects specific language/culture code as first param
routes.MapRoute(
name: "Localisation",
url: "{lang}/{controller}/{action}/{id}",
defaults: new { lang = "en", controller = "Home", action = "Index", id = UrlParameter.Optional },
constraints: new { lang = #"[a-z]{2}|[a-z]{2}-[a-zA-Z]{2}" }
);
Previously I generated my language selection links in the master page, so that they were simply variations of the current URL (with only the first segment changed). Now I need to be able to create the links from within a partial view, that may be loaded dynamically via Ajax and the menu items (countries) are data driven.
That means I need to take the referring URL instead (the actual loaded page) and modify it to have a new language inserted, for each available language. The menu items are all database driven, so only contain the 2 letter language code and the display name.
Googling for "how to separate a URL into controller and action" I found an interesting link here: http://average-joe.info/url-to-route-data/
Based on that link, this is what I tried, but it blows up on a root URL like http://localhost:51176/ or with a full URL like http://localhost:51176/en/home/index. I would have expected it to return the defaults of home (controller) and index (action). Instead I get a Null reference exception.
string path = Request.UrlReferrer.ToString();
string queryString = ""; // Blank for now
System.Web.Routing.RouteData routeFromUrl = System.Web.Routing.RouteTable.Routes.GetRouteData(new HttpContextWrapper(new HttpContext(new HttpRequest(null, new UriBuilder(Request.Url.Scheme, Request.Url.Host, Request.Url.Port, path).ToString(), queryString), new HttpResponse(new System.IO.StringWriter()))));
// Blows up with Null exception as routeFromUrl is always null
string controller = (string)routeFromUrl.Values["controller"];
string action = (string)routeFromUrl.Values["action"];
string id = (string)routeFromUrl.Values["id"];
The idea being I can then generate links with href values like these using the referrers controller, action and parameters and therefore stay on the "same page" (except for the obvious language change):
http://localhost:51176/en/home/index
http://localhost:51176/de/home/index
http://localhost:51176/fr/home/index
What is wrong with the way I have used that piece of code (or does it just not work as I expected)?

Answer 1

Do'h... so simple.
Just needed to supply the path part of the URL only as it uses the current scheme, host & port applied to that path.
string path = Request.UrlReferrer.AbsolutePath;
Also note (valuable tip):
If you follow that example I linked, like I did, you need to adjust the following to use ToString() as they do not cast to string when empty:
string controller = routeFromUrl.Values["controller"].ToString();
string action = routeFromUrl.Values["action"].ToString();
string id = routeFromUrl.Values["id"].ToString();
This will give controller="home", action="index" and id="" as expected! Phew