With a standard T4 template, you can generate any code, but what comes out is part of your project. While you can generate any kind of text, this is really most useful if you're compiling the code that comes out.
With VS2010, you can now use a T4 PreProcessed Template. Instead of generating a text file, you generate the generator. Making the generator instead of the resulting code should give you lots of flexibility with integrating your Java/Ruby output.
Anything can come out of the generator, but I think you still have to write the actual T4 code in VB or C#.