A site that actually already integrates multiple languages in one script, letting users set their preferred language and then showing pages in that language if multiple versions exist, or in the available language, if the preferred is not found. An alias system is used to provide this functionalitiy. Besides that it provides directory-like sections too...
A multilingual wiki mainly for a bunch of webloggers, run by StephanieBooth.
Most users can read both French and English; no attempt at translation or filtering of RecentChanges is made, mainly for technical reasons.
The interesting part about this one is that Hebrew does not have case, therefore the LinkPattern is different, and Hebrew is written right-to-left.
The EmacsWiki has filtering of RecentChanges, but most pages are still in English. See EmacsWiki:OtherRecentChanges. There is a copy of the script using the same page database, but with French translations.
This wiki is for discussing Esperanto Internet projects. Generally everything is written in Esperanto, and if it's considered to be of possible interest to English readers then someone translates the content into English as well.
Wikipedia is actually a collection of separate wikis, each dedicated to a single language. There are twelve that have over 1000 pages: English, German, Polish, French, Swedish, Esperanto, Japanese, Danish, Dutch, Spanish, Catalan, and Italian. An article in one language can be linked to corresponding articles in other languages via specialized InterWiki links called interlanguage links . There is not necessarily a one-to-one relationship between articles in different languages. For example, three articles on the French Wikipedia may be linked to a single English article.
ISSHO Kikaku seeks to unify the world by combining many major languages on one website. Actually, it's an NGO from Japan focused on pluralism worldwide, but its website (portal) is quite ambitious. It's more than just a wiki, but it does contain a wiki (called IsshoCollab?, powered by PhpWiki) as part of its quite diverse menagerie of web applications.
It looks like a group of folks going global.
A pragmatic initiative accompanying the World Summit on the Information Society (WSIS). The goal of ic4 is to develop an understanding of how ICTs can be harnessed to support sustainable development.
Digital Rendezvous is using the OddMuse engine. The user interface and some introductory pages are available in 繁体中文, Français, English.