Stefan, I think the problem with your suggestion is that automated translation is a very inexact science at best (I have this direct from a linguist friend who does it for a living), and there would have to be a huge amount of user input/editing to make sure the links were correct.
Here's an idea. Instead of trying to link directly to the article in the other language, just link to a (to-be-created) *search page* on the other wiki. So we'd simply be creating new links below or above each article, like this:
Search for a different-language version of this article: [[Deutsch]] -- [[Francais]] -- [etc.]
and then we'd also have to create the search pages (which is mainly just a matter of copying code, I guess). We'd also have to translate the above-indented text into the other languages...
Here's yet another idea: don't do anything right now, but when the wikis are all built up as they should be within a few years, go in and *add* (by hand, or partially automated) links to the other-language versions of all pages. That would be a huge amount of work, but it's probably the only practical way to achieve a direct-link scheme.
Larry