For the people who don’t get it: To the Greeks (who primarily spoke Greek and Latin,) Germanic and proto European languages (like old English) sounded funny. The Greeks joked that it sounded like “barbar barbar” which is basically the Greek version of “blah blah blah blah”. So the people who spoke those foreign languages got referred to as barbarians.
It was basically used as a pejorative. It was a way for Greeks to discriminate against non-Greeks.
It’s technically Proto-Indo-European. PIE is the base language that later developed into most of the European languages. It’s a simple language that evolved into the various European languages as people spread out and groups became more isolated. Basically, as they became more isolated they formed their own unique dialects, which then became distinct languages.
PIE is believed to be the root language for Spanish, English, French, German, Italian, Hindi, Urdu, and a handful of others.
Your examples are a bit odd given the context. Spanish, French, and Italian developed from Latin (which you stated the Greeks spoke). English, German, and Scandinavian languages developed from Proto-Germanic. I'm assuming you didn't mean to imply that Latin wasn't a PIE language?
PIE was the language (or languages) the proto-indo-European peoples spoke during their processes of migration into Europe, the Middle East and South Asia (around 6-4k years ago).
So most of the languages from those regions, from Hindi, to Persian, to Greek and English are all PIE, as these are all descendants from the PIE peoples.
We can reconstruct it by analysing these modern languages, their recent ancestors etc. and compare them.
I took it to mean the DM was going to start throwing all the Herculean labors at them, then have the characters wife accidentally poison him, so that he burns himself alive on his own pyre.