How Literate are your D&D Worlds?

[Amechra]

Yeah, I think a smoother system would be to just take a note of how you picked up your languages, as a flavor thing.

You're a Sage? Your grammar is a overly formal, and you might mispronounce a few words that you've only ever seen written down.

You're a Sailor? Your vocabulary in your additional languages is probably going to be pretty darn vulgar.

Stuff like that.

I think the being fluent is more because there's no good way to represent the mechanics of being partially fluent. Handing out say Disadvantage on say Persuasion/Deception checks is both extremely harsh and not particularly realistic as it all depends on the situation, sometimes it would be a penalty and sometimes it would be an advantage. And for example eavesdropping on a conversation in a language where you are only semi-fluent wouldn't technically impact the DC but instead what information the DM gives out.

So I understand why the default is the way it is in 5e, even though I do think you can make fluency/languages/dialects more important.

I actually have a rule for this in my current campaign — High Ingfaltish is a creole between Low Ingfaltish (the language primarily spoken by the common folk) and Sietok (the language primarily spoken by the ruling class). Someone who speaks High Ingfaltish is capable of speaking with speakers of the other two languages (and vice-versa), but you might run into Disadvantage on Deception, Insight, or Persuasion checks that hinge on wordplay or precise wording.

Hilariously, this has allowed my party to communicate with each other despite not actually having a single common language (the Rogue, Ranger, and Sorcerer all speak Low Ingfaltish, while the Ranger and Bard speak High Ingfaltish).