Sorry Juan, Never tested the forum with translatable components. Ive never used translatable myself so if you could list the issues with screenshots on open.silverstripe.org we can see those get fixed.
draft - it searchs author names, title of the post as well as the content of the post. It compares the query to the DB using a match query. See http://dev.mysql.com/doc/refman/5.1/en/fulltext-search.html. You can see how the search function works in code/forum/ForumHolder.php in the SearchResults() function