There have been several thread and comments on the subject. Short reference links list: http://lussumo.com/community/?CommentID=62299 (and the two following comments) http://lussumo.com/community/?CommentID=79708
Before changing anything I'd like to know your thougs?
Multilingual forum are not that common, and implementing multilingual website is complex. I don't think it should be part of the core, but we should make multilingual UI (and comments) plug-in possible, and make installation of multiple forum easy (one language per forum).
For the init_language.php, how will we proceed for the update? We can't just add it to the conf/ folder, it might create problems with people who update their forum via ftp (with ftp, or some ftp clients, sending a conf folder will overwrite the all folder and not just update it).
For the extension translation, where should they be hosted? Since translators and extension authors don't take the responsibility of it, they might need to be hosted in their own folder and not in path of an extension or a translation.