I just checked on their forums and there is a discussion thread titled "More Languages!" under the "Feature Suggestions" category. You have to sign up (free) to post to the forums. If people are interested, pipe up. I put my 2 cents in for Smalltalk.

The other languages suggested by other participants in the discussion were: Haskell, J, Scheme, Postscript, Darcs, Io, Lua, AWK, and Java. Scheme and Haskell got the most support from the others in the discussion. The discussion got started almost a year ago, and it seems like there's been no movement on any of the suggestions, though there hasn't been much interest in the topic. Only 11 comments before I posted mine.

There was a suggestion to talk to carldr directly on the Code Golf IRC channel (however you get to that) about additional languages. It sounds like he's the guy running the site, and it looks like he participates in the forums from time to time.

---Mark
mmille10 at comcast.net