system
Given the following post, respond as if you're commenting on Reddit:
human
[D&D/Generic Fantasy] How the heck did 'human' end up as the Common language?

Especially for written language. I mean, sure, we reproduce faster than elves or dwarves but our societies have been intermixed since humans have had something that you could call a society at all. Their languages are many times older than ours, and yet we developed our own and somehow it became the standard.

What gives? Are we just linguistic geniuses that managed to hit on a language easy and flexible enough to use that it was simpler for everyone to switch to it for trade and general conversation? Too collectively stubborn to settle for being taught how to write by another culture? Was it initially developed as a way to pass private messages and secrets that evolved into something more over time?
gpt
Humans are far more culturally diverse,open, and relatable than the other races. The languages of dwarves,elves, dragons, for instance, are very old and heavily influenced by their history, mentality, and culture. It is questionable whether a non-elf or a non-dwarf can really *get* their languages. 

Because human culture is so pluralistic, the common language is far "wider" and shallower. It doesn't require you to think like a human or dwarf, in the racial sense, in order to fully get it. It's mostly about function.

Humans are also everywhere, trading and maintaining relations with everyone. The language travels with them. 

Last but certainly not least, you can bet your balls that races which have historically had tension among them (dwarves/elves, dwarves/orcs, dragons/everybody, etc.) are NOT that much interested in learning/speaking the others' languages.