mas idzar, you can change into Bahasa Indonesia with this step:
1. open your wp-config.php
2. change the code define('WPLANG', ''); into define('WPLANG', 'id_ID');
for more information about changing WordPress language, check this article : http://www.wikihow.com/Change-the-Default-Language-in-Wordpress
You just install WP languages pack for your case and WP-Pro-Quiz follow the WP language automatically
1. download wordpress language pack here : http://codex.ww.wp.xz.cn/WordPress_in_Your_Language
2. put *.mo and *.po files in your /wp-content/languages/ folder
