How do I generate language X from MPS?

There’s a page on MPS Confluence listing available “base languages” (languages that you could generate your DSL models into). Java, XML, Ant, JSON, R, JavaScript, and others are supported.

But don’t fall into a trap thinking you need to have a language implemented in MPS to be able to generate files in that language! If you want to generate a complex language for which there exists no implementation in MPS, say Rust or Ruby, I recommend that you first use the com.dslfoundry.plaintextgen language that is part of MPS-extensions (also available as an MPS plugin) to generate text directly from your DSL concepts.

Later when you get the initial generation working you can gradually extract language concepts from your plain text generator rules and build your own base language.