I feel languages are strictly the jurisdiction of a setting.
Some settings might only have a handful of languages (like Forgotten Realms), some settings might have thousands. (Today, reallife humanity is understood to have roughly 7000 languages.)
Oh, sure, it should be based on the setting.
But I feel that it's likely that, in a world where people (and their languages) didn't evolve normally, there wouldn't be nearly that many languages. In the real world, a distance of a few dozen between societies might be far enough for a different accent, dialect, or even entire language to develop because traveling that distance would be difficult and rarely needed. In a gaming world, where magic and flying mounts and even flying intelligent people are a thing--and have always been a thing--that distance isn't so insurmountable.
I mean, I'm all for having more languages anyway (or having far fewer, depending on the setting--I can even see a world where there's only a single main language, because everything was created by a single pantheon of gods). I just think having inborn racial languages (that are part of the racial/heritage/lineage traits) is silly, though.
For Forgotten Realms, it seems plausible to me that the "human language" (Common) could become an inter-lineage language of commerce and inquiry. Creating a new artificial language for commerce seems less plausible.
I assume that "Common" is actually a creole of whatever languages the primary traders use. If the biggest traders in a particular are/were, say, humans, halflings, gnomes, and hobgoblins (and for the most part, elves, dwarfs, orcs, etc. sell things via middlemen rather than engage in direct trade), then Common would use words from all of their languages.
(Or if Countries A, B, and C, are/were the primary traders, then Common would have evolved out of their languages.)
I suppose that if one group of humans have "trader" as their hat,
or had at some point conquered most of the known world, then that would explain Human and Common being synonymous. Humans are rarely depicted in that manner, though.