Routing based on Culture(language) selected

public static void RegisterRoutes(RouteCollection routes)
{
    // This one gives you the language
    // Responds to the following url:
    // http://example.com/fr/
    // http://example.com/fr/home/
    routes.MapRoute("Lang",
        "{lang}/{controller}/{action}/{id}",
            new {
                controller = "Home",
                action = "index",
                lang = "fr",
                id = UrlParameter.Optional
            });
    // you can default language here or something just in case
    // user types the following url: http://example.com/
    routes.MapRoute("Default",
        "{controller}/{action}/{id}",
            new {
                controller = "Home",
                action = "index",
                id = UrlParameter.Optional
            });

}

public class HomeController:Controller{
    public ActionResult Index(){
        string language = "fr"; // default language
        object olang = RouteData.Values["lang"];
        if(lang != null){
            // it's possible that lang may be null when user goes to
            // http://example.com/
            language = lang.ToString();
        }
        // Do something now with language... like setting it to the thread
        // Thread.CurrentThread.CurrentCulture = .....;
        
    }

    // Rerouting example
    // http://example.com/home/rerouting -> http://example.com/fr/home/index
    public ActionResult Rerouting(){
        // Redirects to index using french language
        return RedirectToAction("index","home", new { lang = "fr" });
    }
}