I have been told they spoke Greek as this was the “common language” at the time. I tend to disagree. I think they spoke Latin. This, of course, doesn’t mean they didn’t speak Greek as well. Nevertheless, does anyone know where I might find an authoritative answer?
Personally, I think it was Greek (and even a bit of Latin), or perhaps there was an interpreter involved.
By this period in history, Koine Greek, not Latin, was the
lingua franca of the eastern part of the Roman Empire. Latin, though it was the
de facto official language of the Empire, was rarely used east of Italy. It was a newcomer to the Levant, having arrived only with the Roman military occupation of the region in the 1st century BC. Greek, on the other hand, had been around since the 4th century BC, when it was spread as far east as Persia and Afghanistan by Alexander the Great’s army, which left behind ruling elites that Hellenized vast stretches of territory. In the city of Rome itself Koine Greek was in widespread use among ordinary people, and the elite spoke and wrote Greek as fluently as Latin (early Christian liturgies were themselves originally conducted in Greek). All the better educated Jews would have known Greek, and would have habitually used this language when communicating with the higher-ups. Even the uneducated would likely have known at least bits of Greek due to exposure to it in everyday life.
Currently, 1,600 Jewish epitaphs are extant from ancient Palestine dating from 300 BC to 500 AD. Approximately 70 percent are in Greek, 18 percent are in Hebrew or Aramaic, while only 12 percent are in Latin. In Jerusalem itself about 40 percent of the Jewish inscriptions from the 1st century period are in Greek. We may assume that most inhabitants of Jerusalem who saw the inscriptions
in situ were able to read them.
It is quite likely that even Jesus knew some Greek, since Jesus worked as a
tekton (carpenter/craftsman) for most of His life, and since the region in which Jesus grew up was a multi-cultural and multi-lingual area. It is quite likely that He would have interacted with people from Sepphoris, and therefore He may have known at least enough Greek to get by in business with His customers.