You can do this in /ow_plugins/newsfeed/components/UpdateStatus.php
Just a correction.. Its update_status.php actually.
Change the below line
$field->setInvitation( OW::getLanguage()->text('newsfeed', 'status_field_invintation') );
to
$userName = BOL_UserService::getInstance()->getDisplayName(OW::getUser()->getId());
$field->setInvitation( OW::getLanguage()->text('newsfeed', 'status_field_invintation',array('userName'=>$userName)) );
And then in your language page, change text for the keystatus_field_invintation.
What’s happening? to What’s happening {$userName}?
Now if this don't work try {$username} instead. It seems that is what I had to do and it now works for me.