Unions in France generally are motivated to take action by their own self-interest, rather than a desire to serve the interests of their constituents. Many examples demonstrating this could be cited.
I recall a union that forced an IKEA store to close on Sunday (it had been remaining open on Sundays because it made more money by doing so than it had to pay in fines); after the union won in court, the store fired all the employees it had hired for Sunday work. Difficult to see how the union served the workers in this case (especially since the Sunday workers had been getting loads of extra pay for working on Sundays).
Anyway, this incident clearly seems to be some small, unimportant union trying to deny how small and unimportant it is.
There must be some serious cognitive dissonance at work within the union. Pilots are required to speak and read English reasonably well by ICAO recommendations. If they meet those criteria, they don't need documentation in French. If they need documentation in French, then they must not be fluent enough in English to fly safely internationally.
Unfortunately, technical translations tend to be terrible. Good translations are cripplingly expensive. Bad translations are dangerous. The French are very good at producing very bad translations.
It's bad enough that some English documentation is written by French people with a relatively poor grasp of English, as some examples cited here demonstrate. There are many faux amis (words that look the same but mean different things) between French and English, since so much English vocabulary (about 50%) derived originally from French. The confusions are just enough to dangerously impact safety.
One can only hope that Air France pilots are fluent enough in English to not require badly translated documentation in French. The inverse possibility—Air France pilots with such a poor grasp of English that they cannot read documentation in the language—is scary to contemplate.