Hello, Dragons! Can we enter the cave if we promise to remove our boots? Also, do you happen to have any cookies?

My DM had a similar problem with Common, but instead of removing it entirely he basically nerfed it. The in-game explanation is that it's basically a cobbled-together system of hand signs and syllables that are supposed to be used to make trade possible between traveling merchants who don't speak each other's language; as a result, you can't really use it to express anything more complicated than "I want that" or "give me this." Rarely, he'll let us roll if we want to try to convey some important information via Common, but otherwise we're stuck behind a hard language barrier. It's made the game more interesting, not least because of the charades-esque mini game we get to play every now and then lol

https://en.wikipedia.org/wiki/Lingua_franca

It has real historic roots though. A common tongue isn't unrealistic. They once used Sabir or "Frankish" where lingua franca came from, then Latin throughout Europe, now English as a global lingua franca.

I think pathfinder handled common well. It's the default language of the sociocultural zone in which the campaign takes place. In the north Atlantic of earth common is English, in China it's Mandarin, in South America it's Spanish. It's not necessarily everyone's first language, but it's the lingua franca. In universe this means that fantasy Mediterranean is speaking fantasy Latin as common while fantasy China's common is fantasy Chinese

I think it would also be cool for a setting to do something inspired by Plains Sign Language which evolved out of a trade sign language for people who didn't speak each others' languages or something inspired by Esperanto which was intended to be the global workers' second language so we could communicate with each other on similar footing.