How to change Date format according to language in drupal 7.

Hii All,
I m trying to change data format according to selected language in drupal 7..I m using 2 language English and arabic and i want to change date for arabic site . I m using format_date function of drupal but its not working.

Code:

global $language;

format_date($offer->created,'custom','d M Y',NULL,$language->language);

Thanks All.