>>12792526
Egypt, Judea, Modern day Turkey, Greece, Macedoonia, Ptolemaic Egypt, basically the Eastern half of the empire used Greek as the language of trade, then latin, then more eastern languages. Thus the Greek Orthodox Church. It was also quite common in Rome and its surroundings as Official gov orders etc were in both Latin and Greek. It remained so until the Ottomans conqured the Byzantine Empire.
As well, Greeks were generally well educated, muilti linguial, and litterate. Many Greeks dserved as scribes, historians, recorders of official proceedings, contract authors, etc.
It was in the West, Gual, Iberia, and Germany, where the conquered people's did not readily adopt Latin. As things collapsed in the west, the regional Latinate slang, and lack of literacy, became the proto languages we have today.
It was The Church's decision to adopt Latin (and very formal written Latin) for the Bible that maintained it's consistancy in the west during the long dark ages, where illiteracy and rapidly changing regional languages created chaos.