We'd like to have Moodle's system roles in three different languages. At the moment we are forced to use English role names, since the multilang filter does not work at the role rename section of the course settings page.
I'm surprised that this issue hasn't been raised before. Anyway, my colleague created an issue in the tracker with a patch included. Please take a look at it and vote on the issue if you feel that it should be included in the 1_9 branch:
As far as I know, this is the only place where the multilang filter for roles does not work. At the translation input box, the filter works fine: If a teacher translates a role, the translation applies to all three languages, unless he or she uses the multilang span tags.