And the Japanese people are more stubborn about their language. You have to learn Japanese in order to settle or study there. Even many refuse to write their websites in other languages.
But even their kids are still taught English.
Not yet.
A dialect or slang is supposed to remain a dialect.
I can give you an example: In Sicily, at school, If you speak in Sicilian, and your teacher hears you, she will send you directly to the principal's office.
Yeah. And English itself was regarded in the
exact same way after the Norman invasion. Most of the "slang" words in English are only offensive because of an ancient class war between the poor English-speakers, and the rich French-speakers.
In the US, speaking Ebonic fully will also get a kid sent to the principal's office, since it involves swear words more often than not. But I can't speak it. If I tried, I'd sound like a complete idiot
both by other speakers of Standard US English,
and speakers of Ebonic. It has its own set of rules, vocabulary, and grammar that must be followed in order to speak it correctly. Heck, I often don't even understand it very well when I hear it.
For a comparison to your native language, consider this: Italian, and most other Romance languages, is more directly descended from Vulgar Latin than Standard Latin.