Languages are a lot of fun for world-building, but fun-stoppers during play.
Sure, it would be great to haggle with the fungus apes, but dang, no one thought to take the Middle Plains Dialect of Sporetongue.
I’ve seen scenarios that were intentionally built around a group without a shared language that worked (Why are these mysterious mere-creatures beckoning us? Should we trust them?), but never one where checking the available languages on your character sheet and coming up short made the game better.
But you know what is fun? Trying to speak with weird limitations on what you can say.
Especially after a beer or two.
Besides, in a fantasy milieu, where weird species languages exist cheek-by-jowl, there's going to be all kinds of linguistic crossing. You don't need to be fluent in the language of the Balloon-Herders, you just need to share enough loan words with them to muddle through.
So: when you encounter a language for the first time during play, and the GM decrees that there is a chance you know it, roll against the relevant attribute (Intelligence, or Education, or what-have-you).
The degree to which you succeed or fail determines how well you can communicate. Rather than chart this out to specific die results, I’ll just provide a ladder for GM’s to apply as they see fit.
Degrees of Failure
• Critical Failure: Cannot communicate.
• 1 Adjective per communique.
• 2 Verbs.
• 3 Nouns.
• 1 Adjective + 1 Noun + 1 Verb.
Degrees of Success
• You can communicate freely, but don't know the language—you just established a pidgin-rapport with this individual.
• You speak this language. Record it on your sheet.
• You can read and write in this language.
• Critical Success: You are eloquent in this language.
OPTIONAL: Degree of Failure still determines how many words you can speak, but the type of word is determined by the cultural bias of the language. Elvish = Adjectives only. Gnomes = Nouns. Goblins = Verbs.