Do you feel offended when Americans tell you "you have such good english" --- Well it depends on how  he/she is saying. You can easily distinguish from the person expression. If he/she is making expression as if the whole world is falling down then ofcourse he/she is trying to offend you otherwise hell no.

I was in a christmas party a week before. they started talking about christmas and they asked me do you celebrate christmas in Nepal? I said we dont celebrate christmas like you guys do but it is getting more and more popular these days so it is kind of like yes we do celebrate.....and again they asked me --do you guys have SANTA CLAUS in nepal? i said NO. and the one old lady ask me - you guys dont exchanges gifts among friends and family in christmas  and i again said NO. and then she nicely said i just wanted to make sure that you know what is SANTA CLAUS. i didnt get offended by this. is there anything that i should get offended???  she just tried to help me understand .

If you start getting offended by this kind of things, you will get offended every once in awhile. English is not our first language so someway somewhere we lack the knowledge of english.

Americans appreciates when non-english people speak decent english.

So dont try to be oversmart. That is it.