Please check this function
do_register1() in
register.php that is responsible for sending e-mails you should find the from address in headers part as
$headers = "From: " . $main_smarty->get_config_vars("PLIGG_PassEmail_From") . "\r\nReply-To: " . $main_smarty->get_config_vars("PLIGG_PassEmail_From") . "\r\nCC: account@domain.com\r\nX-Priority: 1\r\n";
and the subject is constructed as
$subject= 'Welcome to ' . $main_smarty->get_config_vars("PLIGG_Visual_Name");
So sure the code uses lang.conf elements.
EDIT: the packed files will send an cc to some account you mention too - atp that is hardcoded to account [at] greatinnovus.com - chage it