Thanks for the quick response, Rob!
The Multilang extension in Subversion (an adapted version of one Arnomane wrote, which was itself an adaptation, I think) can do this
I assume you mean this one: http://www.mediawiki.org/wiki/Extension:Multilang (even though it's not from Subversion, the multilang-0.11.tar.gz is apparently only two days old)
That extension sounds very interesting indeed!
with some tweaking, it might be production standard.
Tweaking? In what way? Like adding an option to switch between languages (without having to change the user language setting), or do you mean something (even) more elaborate? I'm not very experienced with PHP (or coding in general), but I'll give it a try.
-- F.