#1 "subject_prefix" in the subject of the email

Hello, I have a problem when I receive the email. The subject of the email appears "subject_prefix" could you check?

Dang, typo. Thanks for reporting it.

This line:

$mail->setSubject($language->get(html_entity_decode('subject_prefix').' '.$order_info['store_name']));

Should be:

$mail->setSubject($language->get(html_entity_decode($language->get('subject_prefix')).' '.$order_info['store_name']));

I'll submit a patch update with this, shortly.

Fixed in the latest commit