"Πότε έχεις έρθει;"
Translation:When have you come?
With the present perfct in English (have come) there should be no indicator of fixed time, like When. So this sentence doesn't work in English, even if its purpose is to used the present perfect in Greek!
But that's not quite right either. “When did you come?” would translate as “Πότε ήρθες;” wouldn't it? To me it feels better to say “When have you arrived?” ...though this sounds strange too.
Example of "when" with both tenses, "When did you sing this song?" When have you sung this song?"
Έρχομαι means both "to come" and "to go" in ancient greek. What made it mean just one of them in this context?