Thats's another interesting point; I still haven't got over the fact that neither UK or American English has an official grammar. The vast majority of languages
do have an official regulatory body that defines the standard grammar, and that is what's being taught at school to kids. For example, in Hungary you can go to a bookstore and buy a copy of the current edition of the grammar and even a thesaurus with all the officially recognised words (which is always a bit controversial, but slang is not considered official anyway). I assume the situation is similar in other countries. Whereas in English the best you've got is the myriad of slightly conflicting style guides written by publishing houses and newspapers. Weird.
I'll talk about the place I'm 1% allowed to talk to, even tough I'm an apprentice, Brazil.
Funnily enough, we don't have an official regulatory body.
We have a multilateral treaty in which all the lusophone countries (even observers from Galicia) tried to "cut fat": everyone abandoned their most obscure and strange rules in order to achieve a minimum unity. It was conceived in 1990, but was only decreed, at least here, by 2008; it is tiny and mostly changes spelling.
Then, our not official regulatory body, but somewhat respected, is, actually, a literature academy (based on the French model). The guardians of our Brazilian dialect are, and always have been, romanticists, poets and writers in general. In a way, they would see the language as a tool, not an end in itself. Even the greatest etymologists are, more than less, members of the Academy, and look after their peers.
Which leads to two interesting cases.
I will present one with a real anecdote. There was a famous Portuguese catholic priest and missionary who preached in Brazilian lands during the seventeen century, his sermons are legendary. To this day, it is presented as a masterpiece the excerpt in which he changed the preposition accompanying the verb believe: exactly the same as English, we believe in god (the preposition gives an idea of stillness); the priest, even though knowing it was grammatically uncommon, started to use the equivalent to believe "to" god (meaning the belief, more than a watertight sentiment, should be a constant active posture). He did that only changing a preposition, as that is lauded as incredible.
Now imagine that same romanticists, poets and writers which don't see language as an end in itself: they see, with some merit, the detour in the norm as more interesting than the norm.
The second fact is that the greatest grammars tend to, more than prescribe, describe what our romanticists, poets and writers were doing in the nineteen century. We are prescribing what we once did, but don't do anymore.