I have noticed that even native English speakers make grammatical errors when it comes to verbs. For example:
Please explain whether these sentences are simply bad English or some dialect.
I would say most of these are possibly just mistakes - people do make mistakes. I can't really speak for dialects/varieties of English in other countries so I'm basing this on UK usage alone. Most of these are totally alien to me.
However, constructions such as "I was stood" and "I was sat" are commonly heard in some parts of England. These are definitely dialect, mostly northern English varieties. I'm Scottish, but we don't use these at all, even in Scots dialects, although I am familiar with them. No. 5 seems to be an example of using "sat" this way, however I'd say it's not a natural example, and I don't think it would be used quite like this in the UK.
As an ESL teacher with certification in marking IELTS written exams, I would mark 1, 2, 3 as wrong, but I can imagine there are local varieties of English where those structures might be correct, though I cannot tell you where. That's to say, they're non-standard, but I can imagine there might be people who speak certain varieties of English who would say they are correct.
I can't imagine a native speaker of any variety accepting sentence 6.
With 4, I read "stood" as an adjective that means "standing", so it's correct.
Similarly with 5, I read "sat" as an adjective meaning "placed" or "located", so it's also correct.
You seem to have a good grasp on standard English. As others have noted, sentences 4 and 5 are valid British English. The others are nonstandard.
Sentences 1–3 can be found in dialects such as AAVE; they should only be used within their dialect and only by those who speak it natively. I haven't heard 6 from someone who wasn't playing with grammar on purpose, but that's not to say it couldn't exist somewhere.
