alt Hacker NewsThe 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...
Last I heard it was closer to 5 millions, which regardless of the amount goes directly into the pockets of some reactionary old dudes.
They don't make a rule book, but they often make blog posts in which they clarify how they want "proper french" to look like.