Since Moodle 1.8 is possible to have one lang dir for each auth plugin. That makes easy to distribute self-contained auth plugins.
But some strings in the admin->auth page are being retrieved from the central auth.php lang file. Those strings are:
[[auth_XXXXXXXtitle]] and [[auth_XXXXdescription]]
This causes that 3rd part auth plugins doesn't show the name nor the global description in Moodle (so they aren't 100% auto contained).
IMO we should move those strings from the central auth.php file to a collection of auth_XXXX.php files and look for them there.
It can be easily done in 1/2 hour of work. If so, please assign it to me and I'll do that for 1.9 (backporting to 1.8 if you consider it necessary).