I updated phpBB 3.0.x forum with MODs to phpBB 3.1. When I go to permissions I can see in Misc tab language keys from MODs I had installed on phpBB 3.0.
Also, I can see there language key from Reputation System I didn't have installed on phpBB 3.0.x, but I tested it as extension on phpBB 3.1 and extension is now disabled. I'm not sure if it is problem of phpBB 3.1 or extension, so I wrote it here.