Don't forget to run the upgrade script ... the new set of language most probably won't without it ...

Make sure to have a look at existing language packs that are available here (so you don't have to do all your own translation). Here's one for German:
http://community.elgg.org/pg/plugins/project/620922/developer/iionly/german-language-pack-for-elgg-1710

Many thanks to all of you! @RACHID: Yes -  I had to change the language file in the profile-manager directory not in the language directory, I had to add the translation of:
       
'profile_manager:user:password_email:text' => "to generate....