This is a little code snippet from php manual:
putenv(\'LC_ALL=zh_CN\'); setlocale(LC_ALL, \'zh_CN\'); bindtextdomain(\'domain\', \'./locale\'); textdomain(
ok, in my case I needed to restart phpfpm by doing service php5.6-fpm-sp restart.
If you are using php-fpm you MUST restart phpfpm in order to clear gettext's cache, restarting apache2 doesn't work.
Hope is useful to someone else.