routes.MapRoute( "DefaultLocalized",
                 "{lang}/{controller}/{action}/{id}",
                 new { controller = "Home",
                       action = "Index",
                       id = "",
                       lang = "en" }
               );

routes.MapRoute( "Default",
                 "{controller}/{action}/{id}",
                 new { controller = "Home",
                       action = "Index",
                       id = "" }
               );

routes.MapRoute( "DefaultLocalized",
             "{lang}/{controller}/{action}/{id}",
             new { controller = "Home",
                   action = "Index",
                   id = "",},
             new { lang = "[a-z]{2}" }
           );