If you wonder how to remove the site name in the subject that is added right after my text inserted in the "AUP_YOUAREINVITEDTOREGISTERON=" in your language ini file, here is the answer:

It is definied in the controler.php file at yoursite/components/com_alphauserpoints. If you check the line 480 you will find the variable $SiteName at: $subject    = JText::_( 'AUP_YOUAREINVITEDTOREGISTERON' )  . " " . $SiteName; Just remove it (shown in red). So the code will be:
$subject    = JText::_( 'AUP_YOUAREINVITEDTOREGISTERON' );