For multilingual ASP.NET MVC 3 web application, I am determining the Thread.CurrentThread.CurrentCulture and Thread.CurrentThread.CurrentUICulture
Thread.CurrentThread.CurrentCulture
Thread.CurrentThread.CurrentUICulture
An alternative place to put this would be to put that code in the OnActionExecuting method of a custom ActionFilter, which can be registered in the GlobalFilters collection:
http://weblogs.asp.net/gunnarpeipman/archive/2010/08/15/asp-net-mvc-3-global-action-filters.aspx