That's true, but the people who wrote the texts
did speak Hebrew, and Aramaic and Hebrew are related (a lot more closely than Chinese and English). Those reading the texts would have had some Hebrew. And when they found that increasing numbers of readers no longer did know Hebrew, they translated them into Greek, which people did speak because it was the lingua franca (sorry) of the Roman Empire at that time.
On the whole, when people who do speak a language write for people who do, but not quite so well, it's likely to be more successful than the instructions mentioned, written by people who don't really speak English for people who do
I think it was not uncommon for scholars to use a 'formal' language for writing and something looser for general chat.
Again, kind of. At the time when the New Testament was written (in Greek), it was the custom for scholarly works to be written in older, classical Greek. Sort of like us now writing in Shakespearean English, because it seems posher.
But the point was that the New Testament writers
didn't do that (because they were just communicating a message and not trying to sound grand), which confused scholars for a bit. It took archaeology a while to dig up other examples of common Greek, so it seemed like a special language for a time. Obviously there are various texts in classical Greek that have been in libraries and so on since ancient times, so the classical language was known and the common wasn't.
