The historical evidence suggests strongly that someone of political or economic influences would be a Greek speaker and reader. Probably the higher on the totem pole would also have good skills on reading and writing Latin. The people in the country and fishermen not as much but in Galilee (of the Gentiles) probably quite some as they bordered and bartered with Hellenistic cities.
It is an historical argument I present to our FRoman FRiends here who assert outside of the city of Rome the early Christians were illiterate bumpkins. On the contrary it was a time in empire history where we see a sophistication of languages amongst the masses.
Paul of Tarsus would not be immune to such an upbringing of multiple languages as well.
I agree that some merchants most likely were multilinguistic or had those resources available to them. When it came to recording those momentous events that were occurring during those days however, I can only envision they first were written down in their native language for a number of reasons.