When is was testing the NL tb3b2 version i noticed that the new folder "archives" (when i select a message to archive) wasn't translated. U used a old tb2 profile.
Exactly which version of Thunderbird are you using? Please copy what is in Help -> About to this bug. Alternately this could be bug 467527 - Restart needed for localized folder name (Drafts/Junk/Sent/Templates name in folderpane tree).
Mozilla/5.0 (X11; U; Linux i686; nl; rv:1.9.1b3pre) Gecko/20090214 Shredder/3.0b2pre This is indeed a dup of bug 467527 after a restart the folder name is translated