"Have you gone fishing again?"
Translation:Oletko sinä taas kalassa?
"Have you gone" means "Oletko sinä mennyt", so basically the literal translation is "Oletko (sinä) mennyt taas kalaan?" and in fact, you can say "mennä kalaan" in Finnish. (We often make jokes about this kind of sentences because it literally means "to go (in)to a fish", so if you say you went fishing in Finnish, someone might ask you "did you fit in there?" :D)
"Oletko sinä ollut" = "Have you been".
Yes, I know that in the English sentence a different verb is used but my question was about the tense. In the English sentence present perfect is used but only past tense is accepted as the answer in Finnish.
There's also a verb kalastaa. Can it be used here? Would it be Oletko (sinä) mennyt taas kalastamaan?
Ah okay, sorry that I didn't understand your question the first time! But that's a good point because they indeed are in different tenses and you can translate that in the past tense in Finnish as well.
- Have you gone fishing again? = Oletko (sinä) mennyt taas kalaan/kalastamaan?
- Oletko sinä taas kalassa/kalastamassa? = Are you fishing again?
But I'm not sure if English-speaking people would ever really use the latter sentence, but in Finnish it's totally fine.
And as you can see from my examples, "kalastaa" is a valid option as well. You can use it either alone or with the verb "mennä". Without "mennä" it, however, can have more of a wider feeling to it. "Kalastatko sinä taas?" can also mean that someone used to fish but stopped that some time ago, and has now started it again, this can also be translated as "Are you fishing/Do you fish again?" in English. But these are more of things that are visible only from the context and nothing you can just read between the lines.