Translation:Are you American?
Actually, "Aren't you American?" would be: 你不是美國人嗎 nǐ bùshì měiguó rén ma?
Slightly different to,"Are you American?" "你是美国人吗？
If we want to be that technical, "美国人" means "American person", so it should already be "Are you an American?".
So, you know, don't personally see a problem with "Aren't you ..." in that they are interchangeable on the English side.
In English, questions and tag-questions are interchangeable. Saying "are you American" means the same as "are you not American" means the same as "you are American, aren't you".
But strictly speaking, if there is or isn't the word "not" in the sentence, and where it is placed, does change the meaning
Oh, they all give a sort of "inflection" to the meaning: sometimes you're saying "you say you're X but I don't believe it", or "I'm pretty sure you're X ... aren't you?". But we can convey most of that using our tone of voice anyway :o)
Ultimately though, they all boil down to the same question, "Are you or are you not an American?" :o)
To which my answer is, "No."
It is correct from context. The program wants you to put "you guys" to make is explicitly clear that you know 你们 is you plural.
are you an american man?
yummy cookies I am in cookie land with my cookie house and my cookie computer