This is a pretty half-baked one, sort of a corollary to my last post. Partial inspiration from Vayra and Arnold.
THE COMMON TONGUE
Is bullshit. There should be lots of different human languages in your setting. A singular "common tongue" is total bullshit, meant to smooth over difficult worldbuilding and actually challenging social encounters.
There are about 8 billion people on the earth, and there are about 6,500 languages spoken, some of which by very few people. Even if with 100 times fewer, with a mere 65 languages, that's still about 64 more languages than are commonly spoken by humans in your average D&D game.
(There's an argument that the common tongue is "fantasy Esperanto" or "fantasy Ithkuil," which is a very cool idea that I would love to see developed but thus far haven't, really.)
Point is, there are lots of lots of languages, and all of them are normal to somebody. That's not what this post is about. Merchants and couriers and diplomats will learn lots and lots of languages here in D&D-fantasyland, but those are all human languages.
THE LANGUAGES OF THINGS
Things can speak. This is known.
On midwinter's eve and the heydays of high summer, when the traveling fairs and circuses and fair folk come into town, there can be sometimes found an elder traveling with them who speaks one of the old tongues. Perhaps run the riddling-contest, or they are the teller-of-tales, or they a watchful impresario. No matter which way, they will occasionally murmur words in those strange tongues, and send shivers down your spine.
What makes a wizard a wizard is their ability to speak to things that normal people can't. This is sorcery, witchcraft, uncanniness—speaking to things that shouldn't talk and then having them reply.
Things can speak. This is known.
SOME OF THE OLD TONGUES
The language of trees, and woods, and ancient gnarled things.
Spoken by elves, faeries, elk, wolves, crows, pines, oaks, elms, roots, vines, creepers, fallen leaves, and acorns.
Wizards who speak sylvan are often called druids, witches, or greenseers.
The language of fire, and heat, and roiling changing things.
Spoken by phoenixes, dragons, djinn, salamanders, fireflies, fire, ash, charcoal, dead wood, stews, smelters, and summer haze.
Wizards who speak phlogiston are often called sorcerers, pyromancers, or conjurers.
The language of stone, and earth, and hard unmoving things.
Spoken by dwarves, giants, trolls, worms, moles, rock, stone, clay, shale, brick, iron, hammers, armor, ancient crusty bread, etched stone runes & glyphs, and cellars.
Wizards who speak terra are often called hermits, geomancers, or runecarvers.
The language of rot, and age, and decrepit dead things.
Spoken by ghouls, zombies, bones, carcasses, carrion, roadkill, tombstones, coffins, dead trees, ancient ruins, vacant houses, mildewing books, spoilt food, plagues, anything preserved in ominous fluids, and chrysanthemums.
Wizards who speak ruin are often called necromancers, haruspices, or heretical priests.
The language of roads, and bridges, and long traveling things.
Spoken by horses, mules, ponies, wagons, carts, wheels, way-signs and -stones, roads, bridges, cobblestones, inns, rivers, backpacks, and certain generous stars.
Wizards who speak via are often called mendicants, wanderers, or sages.
The language of caverns, and the sea, and ancient hidden things.
Spoken by mind flayers, squids, octopi, crabs, the ocean depths, stalactites, stalagmites, limestone, elder gods, caverns, anything petrified, pale blind wriggling things, fear, caverns, pits so far you cannot see the bottom, and whale-bone.
Wizards who speak deep are often called warlocks, occultists, or esoterics.
There are obviously many more old tongues: the language of mirrors and eyes, the language of cities and machines, the language of secrets and murder, the language of coins and laws, the language of blood and heart, the language of wind and thunder, and many, many more. These are just the ones I came up with sitting at my machine here and now.
LEARNING THE LANGUAGE
There are a lot of ways you could approach this. Some languages are taught from master to apprentice, some via a huge collection of dusty tomes, some by divine blessing, some by living far from humans for many years, and some by having some otherworldly thing touch your brain.
Books that contain these languages are very, very dangerous. Those are books that turn ordinary people into wizards.
I'd probably seed these throughout my game world, let players chase after them. Maybe, instead of being a highborn noble or a trained soldier or a devout priest as a starting character, you're somebody who happens to know one of these languages.
USING THE LANGUAGE
I can talk to you and, with the right words, make you do things.
- Here's $100 for your new book.
- Take me out to dinner and I might give you a kiss.
- Give me all the money in the bag, or I pull the trigger.
The old tongues operate by the same measures: you offer something, and they'll do something for you. Difference is, dead bones and wolves and wagon-wheels and ancient caves all have very different desires; some achievable, some not.
Part of what distinguishes one wizard from another is which languages they speak, yes, but what really distinguishes a good wizard from bad is how they use the languages they know.
And, obviously, what they do with that knowledge, now that they have it.