The president of l'Union franรงaise des amateurs d'armes (roughly French Gun Enthusiasts Union) seems to think it's fake on first impression since the law referenced in the opening paragraphs apparently doesn't exist anymore after being re-codified as a different law in 2013. He says in that post that they're paying close attention to the situation and will do everything they can to investigate the veracity of that letter.
The real bit that gets to the meat of it though is specifically exempting "A" class firearms- France has upgraded many semi-auto's in civilian hands that would have been "B" class to "A" and as such, their exemption shows that this cannot possibly be legit and must be a hoax perpetrated by someone who doesn't know the intricacies of French firearms law.
