Has anyone documented what was needed to support Python? I'm interested in implementing other languages, but the lack of documentation makes it incredibly difficult to even find out where to start

Python isn't supported yet...

There's clearly an effort being made, and there's no official documentation on how to support a new language.

Yeah, me and Piotr are working on Python support but there is much work to be done. Definitely there are no docs on supporting a new language, so we just inspect JS IR sources and trying to do something like those but for Python. JFYI: our progress is here: https://github.com/krzema12/kotlin-1/tree/python-backend/python