Officially, only C# is supported so far. Unofficially, any language that can compile to a verifiable managed assembly (the verifiability requirement applies to all dependencies, too!) is good - so you should be able to use e.g. C++/CLI, F#, Delphi Prism...
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…