Every time :( It is sometimes really difficult to learn a foreign language using a foreign language. I am French, and this sentence would translate naturally in French as "Viens-tu à la fête ?" So, of course, every time I see "fest" (or "fiesta" when studying Spanish) I translate with "Are you coming to the fest?" and every time I hear this obnoxious sound telling me I was wrong despite the fact that I actually perfectly understood the meaning of the Swedish sentence. It is an injustice - said with a Calimero voice!
just plain bad English, unfortunately. Phrased that way it almost sounds like you are asking a sexual question to be honest or maybe my mind is just in the gutter. It could be phrased "Do you come to the party" which from still sounds hella weird even if not grammatically incorrect. I can't imagine a situation where an Eglish speaker would say this. It would almost certainly be phrased either as, "did you come to the party?" for past tense OR if you are currently at the party and asking if the other person has arrived yet. You can say "will you come to the party?" for the future.