>Overall, using "du" is acceptable in 90% of social interactions. It's only when talking to people in higher positions or as a courtesy to elderly / unfamiliar people.
I don't think there is a mapping to this in English. I've studied some Spanish and German - You learn about the various verb and pronoun forms based on informal and formal "you". This is a part of the core language, the spec, so to speak.
In English, there is no spec for different levels of formality. There is no universally documented way to being less courteous to bosses and policemen. Saying "sup dude" or "how's it going" is part of the American standard library, not the language.
And to your point directly, "nigga" is incredibly informal and casual, and would never be something anyone (much less a non-native speaker) should ever use unless they know what they are doing. And usually, they should be black, too.
Well it just so happens I am black and I've been using the word most of my life.
Nigga is just "bro" or "dude" but exclusively used among black/minority communities. I realize the word nigga is A Big Deal for white people but really in our community it is used as casually as the word "like" in any given sentence. Interestingly I have even used it with black bosses before in a joking casual way.
You're ignoring the fact that a non-negligible percentage of black people don't want to be called any version of "nigga" by anybody, including other black people.
When I was learning German I read somewhere that English used to have different forms for "you" just like German. Which wouldn't be weird since the languages are closely related.
Yes, in English we fully adopted the formal which is "You" for both formal / informal speech. The familiar / informal was "Thou" - which is a bit weird because now we think of "Thou" as being a bit formal because it is so old-fashioned.
In English, there is no spec for different levels of formality. There is no universally documented way to being less courteous to bosses and policemen. Saying "sup dude" or "how's it going" is part of the American standard library, not the language.
And to your point directly, "nigga" is incredibly informal and casual, and would never be something anyone (much less a non-native speaker) should ever use unless they know what they are doing. And usually, they should be black, too.