User-1827453801 posted
Probably need to assign it to System.Threading.Thread.CurrentThread.CurrentUICulture in your applications BeginRequest event.
You can read it from HttpContext.Current.Request.UserLanguages. Its a string array in order of the user's language preference. For example: ["en-AU", "en-GB", "en-US"]
Just take the first value and use it to the create an instance of CultureInfo.
http://msdn.microsoft.com/en-us/library/ky2chs3h.aspx