I was looking at some common European languages to see if I could improve on Colemak. I found a couple of small changes.
For German and French, switching U and O helps. Especially German, because O is rare in German.
Switching Y and Z could help in German. That would put Y in its original position, plus Z is more common than Y. I'm not sure about IZ/ZI frequency though.
In Spanish, switching T and D helps. D is a lot more common, plus it leaves T in its original column.
Switching K and J could help in Spanish. K, H, and J are all rare, so the right index is a bit underused. Moving stuff around could probably fix that.
My typing speed record: http://hi-games.net/typing-test/watch?u=493