Some projects, like Wikibooks and Wikisource (not to mention Meta), don't have major naming conflict problems. But it would help a great deal if it were possible for users to set their preferred interface language in their preferences and for language category tags to set the interface language as well (so anons visiting a page with a French language tag will have their interface switch to French; &lang=fr in the URL would trigger the same thing as well).

-- mav