We have as much responsibility to usability as we do to political correctness.
The best solution would handle both.
The worst solution would hurt usability and encourage language balkanization.
What are the parameters of the situation?
1) www.wikipedia.org (and its minor variants wikipedia.org and wikipedia.com) is and will forever remain the primary url.
2) Wikipedia is currently owned by an American company; it was started in English; the English Wikipedia is orders larger than any other, English is the lingua franca of the current times and of the Internet. All these may change but are true now.
3) We desire all the language Wikipedias to be on equal footing.
Note that, for 3) to mean "equivalent in content", there would have to be some mechanism to compensate for real-world differences in the degree of participation in different languages. There will always be more English than Icelandic speakers, etc. A perfect such mechanism would be expert-quality automatic translation.
That out of the way, let me suggest that changing URLs should only be a minor component of dealing with 3, not a primary focus. More effort should be put into building the cross-link capabilities, perhaps with some automatic dictionary translations. The wikipedias should all be running the same software. There should be the option of having Recent Changes show changes from any array of the languages, so that for a French contributor fluent in English, his Recent Changes (and thus his Wikipedia, to a large degree) looks like a French-English Wikipedia.
I really think focusing only on the URLs is making us miss the big picture.