You can use the session variable XSession.Session["language"] that stores the selected language, e.g., "English" or "Spanish".
Examples
Getting the value of selected language
Use the following function for this purpose.
MVCFunctions.Echo(CommonFunctions.mlang_getcurrentlang());
Setting the current language
To change the current selected language assign a new value directly to the following session variable:
XSession.Session["language"]="English";
See also:
•Localizing ASPRunner.NET applications
•Save user data in session variables