GnomeWorks
Adventurer
And a little more spilled ink than the current lists with maybe a bit of rules on partial fluency through adjacent language understanding would be better than what we have for verisimilitude. And not terribly expensive.
There's no good way to do this that is satisfying, reflective of how language acquisition works, and low complexity.
It's not "a little more spilled ink."
One of the things a DM has to do IMO in worldbuilding or campaign prep is rebuild the language table/list to suit that particular campaign. Thus, if you don't have Pomarj in your setting then obviously that language won't appear on your list.
Forcing another task onto new DMs who may not be as much of a linguist as Tolkien strikes me as unnecessary busywork.
The way it is now is fine. No, it's not entirely sensible, but then lots of things in core don't hit that bar, so it's a big whatever from me.
That's just it: I don't think it gets the notion across nearly well enough, mostly due to the default that all PCs (and a shocking number of NPCs) automatically and must know Common.
I don't have a problem with removing Common. I also don't have a problem with it existing. But if it were removed in favor of say a small handful of generically-named "trade languages," or whatever, I wouldn't be opposed to that.
Fair enough. Just one more thing to add to the "worldbuilding" chapter in the DMG; a chapter that really should be its own entire book.
Some kind of "advanced" DMG, perhaps. I'd be down with that.