localisation error

There is an error at the localisation. You need to add the t function to this area:

At the function flag_friend_preprocess_flag

case FLAG_FRIEND_FLAGGED:
// Make this link into a remove link with
$vars['link_text'] = t($vars['flag']->unflag_short);
$vars['link_title'] = t($vars['flag']->unflag_long);