I realize it's sometimes not considered cool to point out competing projects, but the OneLang project FAQ explicitly says that it's a proof of concept, not ready for production use, with no documentation, and may never be finished.

https://github.com/koczkatamas/onelang/wiki/FAQ

OneLang does seem like a nifty project, but given its current state, it seems pretty reasonable to point toward Haxe for anyone interested in something similar that has been around for years, well documented, and used in production by many teams.