Dungeons and Animals
In addition to languages known innately by your race and class, you can learn additional languages based on your intelligence score. Learning a language takes a significant amount of time studying, which can be done in between adventures and is accelerated with the help of tutors or quality study aids. The maximum number of additional languages you can know is equal to your Intelligence score – 10.
You may start your adventure with a number of additional known languages equal to your Intelligence modifier. However, if you wish to know an exotic language, it will cost twice as much. (For example, if your modifier is +2, you may know either two additional standard languages or one additional exotic language.) You may not learn secret languages such as Druidic or Thieves' Cant in this way.
Common – Language spoken by majority of civilized society members and known by many of the less civilized as well. It is well suited to express both simple and complex ideas.
Verdant – Language spoken by races with woodland origins. It's composed mostly of chitters and squeeks, and is more apt for conveying feelings and impressions than specific nuanced thoughts. It has several regional dialects, including Boreal, Broadleaf, and Tropic. If two people are speaking different dialects of Verdant, they are able to communicate verbally with only some difficulty. However, all the dialects use different scripts, so reading written correspondence of an unfamiliar dialect is very challenging.
Aridi – Language spoken by races with ancestors from deserts and plains. Most of the sounds are based in hisses, grunts, and growls. Depending on the species of the speaker, the accent can be hard to parse, as a snake person speaking it would sound quite different from a lion person.
Aquan – Language spoken by aquatic and amphibious races. It can be spoken underwater by those with gills, though it can be very hard to hear. Mainly consisting of glubs and smacks, it can be very hard to speak if one is not equipped with the right biology.
Auran – Language spoken mostly by feathered folk, using primarily the sounds of clicks and squawks. It's utilized most often to communicate at high altitudes when wind is rushing by and tone is indiscernible, meaning it carries quite well.
Abyssal - Language of demons and evil planar outsiders.
Celestial - Language of angels and good planar outsiders. When spoken, it sounds as if the speaker is singing a beautiful choral melody.
Deep Speech – Language of inscrutable monstrosities and horrors. Though mostly sounding like a series of whispers, essential to the comprehension of the language is hearing what direction the whispers originate from. To speak this, a normal creature must constantly throw their voice in myriad directions.
Draconic - Language of dragons, as well as lizardfolk and similar monsters.
Goblin – A language spoken by goblins, hobgoblins, orcs, giants, ogres, and other similar monsters. Mostly consisting of grunts and screams, specificity is lacking in this highly contextual language. Depending on the situation, things like verb conjugation and tense can be ignored.
Infernal - Language of devils and creatures that have a hellish affinity. Inherent in this language are many magicks that bind the speakers to their words, forcing them to adhere to what they say. However, those who are particularly familiar with this language can use careful word choice to skirt around these obligations.
Primordial - Language spoken by elementals and creature that hail from the elemental planes of water, earth, fire, and air. There are four dialects of Primordial, one for each element.
Sylvan - Language of the fey. As whimsical as the fairies and pixies who speak it, Sylvan can be fluid in its particulars. Sometimes a speaker may say one thing, but upon later reflection remember saying something entirely different. Part of speaking this language is to include lots of extraneous details so that there are many elements of what you say that may change while not affecting your overall point.
Undercommon – A language used most often by subterranean peoples and many of the monsters that dwell beneath the surface of the earth.
Some exotic languages require specific magical biology to speak, and as such even if you fully comprehend the language, you may only be able to barely speak any of it. For example, speaking the fire dialect of Primordial requires actively making the sounds of a crackling flame, which may not be possible for creatures who can't light their mouths on fire at will.
Druidic - Language known only to Druids.
Thieves' Cant – Less a language and more of a code used by thieves and rogues to communicate simple messages by disguising them in seemingly normal conversation. Also has a system of written symbols that convey very basic information while appearing completely unremarkable to anyone not privy to the code.
There are myriad other languages that are specific to their respective species. Most intelligent creatures have their own system of communication that these use with each other. Some examples are Bullywug, Gith, Gnoll, Sphinx, and Worg.