The D&D 2024 Player's Handbook explains why everybody—in every world—speaks Common

One of the most glossed-over aspects of character creation just got more interesting in the Dungeons & Dragons 2024 Player's Handbook: language selection. 

Unless you have a polyglot Dungeon Master that happens to be an Oxford Professor of English Literature specializing in Indo-European languages (whose name rhymes with J.R.R. Trollkien) then language selection probably carries very little importance in your D&D campaign. 

Does your DM not want you to know what the courier's letter says? It's probably written in an ancient and unknowable tongue, at least according to the DM. Does your DM want you to know what the courier's letter says? Then it's probably written in Common.

Why is Common so common? Even back in the 5e Player's Handbook it says that "You can speak, read, and write Common." Is it really that important? I mean, they copy-pasted that sentence into each and every one of the 5e PHB's nine races, so it must be important, right?

Yet it was nearly pointless to take up precious space on your character sheet by writing it down. In fact, Common only seems worth mentioning if your character doesn't speak Common. A character that doesn't speak Common would make for some entertaining roleplaying scenarios—as well as (and this is probably closer to the truth) a whole lot of tedious interactions instead.

In the new D&D 2024 Player's Handbook, it doesn't copy-paste that phrase about knowing Common into every species selection. Now in Step 2: Determine Origin of creating a character, there's a line that says:

Every player character knows Common, which originated in the planar metropolis of Sigil, the hub of the multiverse.

Well I'll be. We have the Planescape: Adventures in the Multiverse books to thank for that. Common is anywhere and everywhere because it stems from the very center of the D&D multiverse. Sigil, City of Doors, a dense urban region filling the inner ring of a donut (or "torus" if you're fancy), spinning around an infinitely tall spire of rock. A city run by the unspeaking Lady of Pain who apparently makes sure everybody speaks a lingua franca by making them sit up straight and pay attention in Common class.

The only other time Common is mentioned in the 2024 PHB is under the Human section of selecting your Origin:

Scholars dispute the origin of humanity, but one of the earliest known human gathering is said to have occurred in Sigil, the torus-shaped city at the center of the multiverse and the place where the Common language was born.

Oh, and the 2024 PHB also added Common Sign Language to the list of Standard Languages because Sign Language is dope and you should learn some of it. You'll be surprised how much Sign Language makes sense. Plus your characters need a non-verbal way to communicate when you're three torches deep into that Keys From the Golden Vault heist and you need to wordlessly tell the Kender in the party that taunting the polearm guards would be inconducive to the success of your mission.

So don't fret if you're about to become a world-hopping traveler and take your Dragonlance character over to Greyhawk, or your Forgotten Realms character up into Spelljammer. Someone there—most people there—will be speaking your language.