Hello, I'm writing to hopefully make things clear for everyone :)
The standard way to do translation is to submit patches to central Subversion repository, which is where up-to-date version of MediaWiki lives. Rob made his extension available in the repository, so you can download it from there and have it commited back there. Now there are several ways ho to accomplish the commit. Most of us can't do it, because we're not developers, therefore we don't have write-access. We need to ask one of the developers. The usual way would be to submit a request using Bugzilla, attaching the translated file (usually a patch for it). Other way is to contact a developer directly, i.e. using IRC or e-mail.
Now the most convenient way for _translators_ is to do the translations on Betawiki, because it provides a convenient interface. We don't have to mess with .php files and patches. Nikerabbit, who runs Betawiki and who is a developer, will do that for us.
Now to the first question - "Will these messages be available at the Beta-wiki ?". The answer is - no, for now, it won't. The reason is, that Nikerabbit is for now not willing to mess with extensions, which are separate pieces of software from MediaWiki. At least that's what me told me last time I asked. You have to ask him this question to get a qualified answer. Rob Church has nothing to do with that. Nikerabbit runs betawiki.
You can still do the translation the usual way, though. Download i18n files for an extension from Subversion. You can use the web interface ( http://svn.wikimedia.org/viewvc/mediawiki/trunk/extensions/ ), though it may sometimes screw up encoding. Then make your translation and file a new request at bugzilla ( http://bugzilla.mediawiki.org/ ), where you attach the updated file.
So please, translators, don't blame Rob Church that he doesn't know how we do translations. And please, Rob, don't blame translators that they have no idea how software development works. We're cooperating here! :)
If there's something that i didn't put clearly enough, please, ask. ~~helix84