My boss is one of the most intelligent people I have ever met, but English is not his first language; he often misuses English idioms or misunderstands background American culture that we take for granted. For example, he once said "you'll never know" instead of "you never know", and didn't understand why the other person reacted as if he had singled them out. According to those who have been with the company longer than I have, he has admitted to being embarrassed by this to the point he will avoid speaking.
Of all the people in the company, I probably work with him most closely and frequently. He is a very easy-going, genuine person, and it's unfortunate when others don't see that. I genuinely just want to help him fit in, but he's still my boss, about 10 to 15 years older than me and vastly more intelligent than I am. I wouldn't want it to come off as petty one-upmanship ("Sure you're smarter than me, but did you know this?! Thought not.") or an insinuation that his English is truly terrible, given how sensitive he seems to be about it. Should I even bother?
EDIT: My question is not a duplicate of the one listed, because it focuses more about being understanding of an ESL foreigner and the social implications of that, and not on someone whose first language and cultural background are shared by the corrector.