What is "Standard English"?
There are no rules.
English does not have a governance body such as the Spanish Real Academia Española or the French equivalent.
We are "taught." The teaching, however varies.

Is The Oxford English Dictionary followed in "Standard English"?

Certainly most people, even university educated, vary in usage. People who trumpet "Standard English" never make clear what they have in mind.

Grammar, perhaps, is the only common denominator, although there are a few variants here as well.

Words are not standardized. Most people in the UK write recognise rather than the OED recognize, vary in the use of napkin, use plural verbs with collectives, etc.
Pants in US and Canada means trousers; to most in the UK this means an undergarment. Vest, knickers and other words for personal attire have different meanings in the English-speaking sphere.

The dominant culture, American, has its own "lingua franca" and Australia, New Zealand, Canada, England, Scotland etc., have their own.