You might tell your DM to look up Sabir, where the term Lingua Franca came from, the “Frankish tongue” which wasn’t really from the Franks.
This is where the idea of a common language comes from. Sabir was a simplified pidgin mix of Mediterranean languages so traders could communicate. They still spoke fine but didn’t conjugate verbs, used Me/you a lot without different forms (myself, I, yourself, them, they, etc).
Sabir was a Mediterranean lingua franca, then Latin for 1500 years throughout Europe. Now it’s English. The idea of Common in D&D comes from Westron or “the Common tongue” in LotR which D&D was heavily inspired from, which was basically written by Tolkien so that his constructed languages had a reason to exist. He was a scholar of languages, and the idea of a common tongue comes from actual history. He wasn’t just making it up. Something like that would likely exist in a Fantasy world with lots of trade.
Some people definitely agree with the xenophobia. That sort of anti immigrant ideology is on the rise outside of the US too. They might not like Trump but also not quite fully disagree with what the MAGA people stand for.
I mean ffs people are now finally getting sick of Trump, but not because the damage they’ve done with deportation but because they’re spending money on war and food and gas prices went up as a direct result. Some of the people that are anti Trump these days just care about their bottom line.