Василий

//more general route
        routes.MapRoute(
            name: "{lang}",
            url: "{lang}",

            defaults: new { controller = "Home", action = "Index"  }
        );
        routes.MapRoute(
            name: "{lang}/category/{category}",
            url: "{lang}/category/{category}",                
            defaults: new { controller = "Home", action = "Index" }
        );