The Académie française does not edict official rules. Nobody does, there is no official governing authority for the French language but the ministry of Education is the main reference in France. Their rules are generally used for official documents, and since they decide what gets taught to children that's what becomes the normal language when the children become adults.

Also, it costs about 1 million euros per year[0], I wouldn't call that very expensive on the scale of a country like France. Even if it's absolutely useless.

In practice, zero is normally singular in French unless you want to show that there is none of a number of things ("zéro produits artificiels", "zéro émissions").

[0]https://www.liberation.fr/checknews/2017/12/14/bonjour-combi...

Would anyone, even a member of the Academy, write "il y a 1.33 femme pour chaque homme"?

What would it mean for x to be negative, if x is how many of something you have?