changing language for users

How to change the language setting for each user .
Settings.json contains user settings and default settings. If I want to change a language from english to tamil how I need to do for a particular user?
You can provide option to the user to change the default language of the application. When the user chooses a new language, please call the below API to persist the new preference.

var json = {}; = "setUserPrefs";
json.callBack = setPrefCallback;
json.userprefs = {"LANGUAGE":"TAMIL"};

Subsequently, the application launches in the new language provided it is build with that language. The current language can be accessed using the variable apz.language.