Perhaps I'm only stating the obvious here, but I would suggest the following guidelines:

• Local developers can make always updates in local parts of the code, for updates in the common part of the code they should ask Lee's permisson.
• When a new version of the code is installed for the English Wikipedia then this should be announced (on Wikitech-l) and then installed on local Wikipedias by the local developers as soon as possible.
• Local developers are responsible for putting local bug-reports on something in the common code in the Sourceforge bugtracker.

It should be simpler than that. There is only one codebase, and it contains only one language-specific file: "LanguageDe.php", "LanguageEs.php", and so on, all of which are kept in the single codebase. There'a also a "LocalSettings.php" for each install, but that doesn't change once installed. Those files can be changed at will by anyone without affecting the English wiki, and should be. The code is also organized so that if, say, I add a special page and update the code of the foreign version, that special page will appear in the foreign version, but with English text; they can add the translation for that page at any time, no coordination needed.

I also don't have any problem with Brion, Magnus, you, and other developers doing direct checkins. I'd prefer that such new checkins be tested on my server before installing them on the wiki server, but even there I can see small bug fixes not wanting to bother.

In short, I don't think we need to worry about coordination unless one of the groups decides to "fork" the code for some reason, and in that case I'd try to talk them out of it, but if they really wanted to do it, they're free to, and then they'd definitely be on their own.