Posted this answer to a similar question/comment:

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We (I work for Nanobox) listed all the languages we hope to support mainly as an invitation to collaborate. We admittedly do not specialize in all programming languages. Engines are open-source and those who do specialize are invited to create engines for each language. We'll even create the engine for you. We just need to know what the engine should look for and how the environment needs to be configured.

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The library of engines is in its infancy and we're working to expand it. You're absolutely right in saying that the list of engines is "aspirational". Anybody can build and publish new engines. Any help you can provide would be greatly appreciated.