We've recently started moving many of our extension code into the MediaWiki Subversion (SVN) repository so that their development can benefit from the input of all those working on the main code-base and other extension developers who take an interest.
This has already proved to be a very productive move, for example, the EmailArticle extension was moved across one month ago today and has already been internationalised and messages fully translated for 14 new languages; Arabic, Bulgarian, Esperanto, French, Galician, Luxembourgish, Malayalam, Marathi, Dutch, Norwegian, Occitan, Slovak, Swedish, Vietnamese!
