If I know English isn't their first language and I get the gist of what they're saying then no. I'm not their teacher. I do find it a bit rude, to be honest.
I guess it depends on how you say it, like someone else said. Otherwise, it can come off rude. At least they are making an effort to learn another language.
It depends on how you go about it. If you're trying to be helpful and say it in a nice way then it's fine I guess. But let's get real most times people are straight up rude about it and call the person an idiot and belittle them and that's not cool.
Definitely not. If I am speaking a foreign language and make a grammar mistake than I would want somebody to correct me so that I don't embarrass myself and so that I can learn something.
