I know that you can import language packs in the Admin-CP using a WBB. I think this is a nice feature.
What do you mean by 'import'? Uploading it through ACP or the ACP gets it from mybboard.com?
Maybe both? show the available packs from mybb site and an upload field?
Problem is MyBB using php files for the languages, and then you would have to have the whole language folder 777 chmodded for it to work.