[chvrchbvrner]

It's called Osiris and they state it "is a mostly declarative programming language, similar to Prolog" [1]

I think you get access to their engine if you buy one of their games through steam and you can mess with Osiris (not sure if that's still true for BG3, but it was the case for Divinity: Original Sin).

[1] https://docs.larian.game/Osiris_Overview

[talideon]

I believe you have Osiris access at least since Patch 7, when they opened things up to modders.