Who actually wants this? People want good libraries for doing this with the languages they already use, not to have to make compromises just so they can have a microservice. Notice that the front page gives lots of examples of the servicey parts of the code, but absolutely no examples of what the business logic looks like. In fact, even in the documentation, the example code is minimal and trivial.
That's exactly my first thought.
But: I'm currently working on a distributed Webassembly runtime. Jolie seems like a great way to describe your whole system.
For each service the executed code would be a function exported by a Wasm module, written in the language of your choice.