Im a layman on these topics but I often think an intermediate translation to a controlled natural language should be invaluable (e.g. you can train a NN to translate, and a human can verify it without knowing about coding).

I've considered it, but from interactions with lawyers it seems that you don't need to put that degree of sophistication into the syntax for lawyers to be able to read and review the code. Turns out semantic features like the possibility of splitting the code into base case/exceptions and definitions under condition seem more important.

Catala is just a functional language under the hood, and its syntax is very basic (it has an LR(1) parser) with just verbose keywords.