This design forgoes my second biggest usage of Wikipedia (and I suspect it's a big use case for other multilinguals). (My primary usage of course being reading and enjoying the vast content.)

I often use Wikipedia as a high quality word translator. I study at a Swedish speaking university which requires that a lot of the written material I produce is of course in swedish. Whenever I'm writing a comp sci text and I wonder what in gods name a "morphism" is in swedish I just look up the english article (http://en.wikipedia.org/wiki/Morphism) and hover over the swedish language in the sidebar and voilà I've got a peer reviewed translation (peer reviewed because it probably has sources in both languages, in most cases).