> Truffle is a framework for writing interpreters with annotations and small bits of extra code in them which, when Truffle is paired with its sister project Graal, allow those interpreters to be converted into JIT compiling VMs … automatically.

> If Truffle is a framework for writing AST interpreters, then Graal is the thing that makes them fast.

> Truffle provides a language interop framework called Polyglot that allows Truffle languages to call each other

Indeed, I remember stumbling across it years ago while looking for a way to develop Flash games without Adobe Flash Professional. I never got around to actually try it but I keep seeing it every now and then, even saw a couple of books about it in a physical bookstore some years ago. It was the first thing that popped to mind for me as well when I saw that OP title mentioned write code in multiple languages at the same time.