There is an example of the US tax code on the landing page of website (https://catala-lang.org/en/) so they actually seem to have also tried the language on English-written law!

Maybe that was done to prove the point that the language, unlike most other programming languages, does not have any built-in English assumptions?

Also I think the examples are actually quite comprehensible even to non french speakers.

They aren’t. Also, it doesn’t seem to make sense to use only French examples in midst of English written text. I don’t think its a major problem of course and main project page contains English examples, I just found that funny.