Americans, is it difficult for you to understand people who are not native speakers and can make a lot of mistakes?

Depends on how traveled they are. Personally, if someone is speaking any sort of broken English, I can understand them just fine. But I’ve met Americans who can’t even understand a BBC show.

Don’t sweat the weird grammar and conjugations – English is a crazy confusing mix of languages. Just making the effort is usually appreciated. Except by a few who will somehow feel the need to correct you so they can feel superior in the one and only language they’ve learned, probably incorrectly.