We don’t know very much about classical antiquity despite living in its ruins. Most of what we think we know is from romantic reconstructions dating from the early modern era.
However, I don’t think we can know even that if we don’t recognize the interrelationships amoung country, identity, and language in antiquity. “Egypt” is where Egyptian was spoken and it was spoken by Egyptians. “Rome” is where Latin was spoken and it was spoken by Romans. “Gaul” is where Gaulish was spoken and it was spoken by Gauls.
We can be pretty confident that Picts and Scots spoke different languages because the Romans distinguished between them and they would have made that distinction based on the language they spoke. My guess would be that the ancient Scots spoken a Goidelic language (like Irish or Scots Gaelic) while the Picts spoken a Brythonic language (like Welsh or Cornish) but that’s just a guess since we have no attestations of the Pictish language. It might have been a linguistic isolate (like Basque).
Now go back and read the Hebrew Bible. You’ll get a very different impression about stories, like say the “captivity in Egypt”. Just as a side note to the best of my knowledge the earliest attestation we have of Hebrew is that it was apparently spoken in a Persian fort about 2,500 years ago in Upper Egypt.