Most but not all laws in France are like that. In fact, some of the laws applied in France are written... in German and aren't compiled in the codes. There is a whole institute (albeit small) dedicated to studying and make those laws[1].

The case happened to me when I searched for the original text that said a worker have to be compensated in full for "short" sick leave, and what I found was a very short text in German. Hopefully the company I worked for complied with law after consulting its accountant.

[1] https://idl-am.org/