Have a look at the hosting page for the green plus sign, whose intended purpose is to make voting less language-specific. Its purpose is intuitive to most people, and had darn well better be intuitive because both the description for the symbol and the explanation of why it's edit protected are available only in English.
It doesn't take long to find a lot of little templates in use over at German that aren't German. And if you want to create a new account, even the security text to prove you're a human being is English only. That's great for an Amerikanerin like myself, but suppose I came from Dresden and hadn't been educated in English as a second language.
What's especially disturbing is that German is the second largest language edition of Wikipedia. It has nearly 800,000 articles, yet these language barriers are still so easy to encounter. That tells me Gerard is probably right on target when he says it's a significant barrier to growth at smaller startup Wikipedia editions.
It's hard enough to explain to a native English non-Wikipedian what a wiki is, and that it's really all right to click that "edit" button. Now imagine the challenge of persuading that friend to edit for the first time if that button said "edit" in Swahili, and if half the commands and all of the templates were in Swahili. Well the actual Swahili Wikipedia has that problem in reverse. As of this writing it's got 7383 articles, 9 administrators, and 1110 registered accounts. And it's the lingua franca for most of East Africa. I'm not certain how localized that Wikipedia really is, but it's a darn safe bet Swahili is less localized than German. If we want viable Wikipedia projects to really serve the world, we need to start by providing menus that the world can understand.