alt Hacker News> speak about the grammar for a language/dialect we imply a prescribed "correct" grammar
Not prescribed, rather observed. At least in English where there is no language authority and dictionaries present usage.
The situation is even stranger in Norway where there is a prescribed form but where dialects have essentially equal rights so that the prescription really applies only to formal written Norwegian.
From what I experienced, "proper" English grammar is absolutely prescribed at schools, and "poor grammar" will consistently and very predictably get you point deductions, regardless of whether linguists would accept your grammar as valid.