Hello,
This mail is sent trough "paypal.php" with this code :
$order->mail_status=$statuses[$order->order_status];
$mailer->setSubject(JText::sprintf('PAYMENT_NOTIFICATION_FOR_ORDER','Paypal',$vars['payment_status'],$dbOrder->order_number));
$body = str_replace('<br/>',"\r\n",JText::sprintf('PAYMENT_NOTIFICATION_STATUS','Paypal',$vars['payment_status'])).' '.JText::sprintf('ORDER_STATUS_CHANGED',$order->mail_status)."\r\n\r\n".$order_text;
$mailer->setBody($body);
$mailer->Send();
So you'll just have for example to change the
translation word "PAYMENT_NOTIFICATION_FOR_ORDER" and "ORDER_STATUS_CHANGED".
Hope this will help you.