As could be expected, there are a wide variety of languages spoken on the planes. While planar trade, or "common", can be found just about anywhere, for most beings it is learned only as a second or third language.
Amongst the mortal languages, classification is a surprisingly complicated affair. Contrary to the expectations of many prime worlds, mortal languages such as elven or dwarven have evolved independently throughout the Material Plane in such a way as to be quite similar to one another even across different worlds. Whether due to the influence of deities wishing their followers to be mutually intelligible across the Prime, influence from extraplanar beings, or the effects of cross-sphere trade across Wildspace, these languages have largely converged across the Prime by this point; thus, classifying them into families across multiple worlds is fairly frustrating for those attempting the task. The planar languages are thankfully spared this problem; furthermore, the long (and often limitless) lifespans of planar species greatly slows the rate of change in languages, allowing even mortals a good glimpse at the inter-relations between dialects hundreds of millennia old.
The below list is separated into the known major language families, and subdivided into lines of descent as recorded and derived by linguists amongst the Fraternity of Order and Society of Sensation. Names are officially recognized translations into Planar Trade, with common names following where necessary.
- As the plane of Air is the most populated of all the Inner Planes, Auran tends to serve as something of a trade tongue itself amongst the Inner Planes. Even the planes of Earth occasionally find it used for such a task, though quite rarely, and never within earshot of the dao.
- For a variety of reasons, Draconic has essentially become the erstwhile language of the arcane research community. Study and research into arcanism is performed in Draconic even more so than Common.
- Least Baatorian
- This caste of Baatorian is spoken as a primary dialect only by the spinagons. It is a simple language, used to convey basic commands and concepts. Usage of Least Baatorian is considered an insult and mockery to the one being spoken to, implying you consider them of low intelligence and no subtlety. In use, it's a harsh, barking tone, having evolved largely for shouting commands across a battlefield.
- Lesser Baatorian (Infernal)
- This dialect is the one known by outsiders as the baatezu tongue. While more pleasing to the ear than Least Baatorian, it still has a sharp, commanding tone to it. This caste of the language is the first to hold the noted complexity of the language, with double-meaning, innuendo, and even wordplay innate fixtures amongst this and all higher castes. All contracts with non-baatezu are required by baatezu law to be written in Lesser Baatorian.
- In written form, the language consists of 33 purely-geometric symbols, plus a second set of characters for numerals as well as logic and mathematical symbols
- Formal Baatorian (Malbaogni)
- Somewhat beyond the capability of most mortals to learn, Malbaogni, or "Formal Baatorian", is a multi-layered language relying on the ability of the baatezu (and other lawful beings) to see and predict patterns in order to communicate meaning. Speech in Formal Baatorian is even more layered than that of Infernal, and deriving the natural flow of conversation's logical end is almost required to understand even the smallest bits of this dialect. A skilled baatezu can carry on an entire conversation from nothing but the beginnings of sentences, predicting the endings based on nothing but his knowledge of his "opponent". A Malbaogni exchange is oft compared to an odd mixture of song and contract, melodic yet rigid.
- Courtly Baatorian (Mabrahoring, High Infernal)
- Almost knowingly ridiculous, Mabrahoring is used only by the pit fiends and other baatezu nobles. Taking Malbaogni to its logical extreme, Mabrahoring is used more to challenge one another than for any true communication between baatezu. With the specificity of a full legal arrangement in every sentence, it is nearly impossible to hold traditional conversation in any mortal sense in this caste. Mabrahoring is so elaborate that its written form is in fact the origin of the runic inscriptions first used to form summoning and binding circles; the lines of symbols not words of power, but simply an explicitly well-formed argument as to why the baatezu in question should remain within. Even amongst the highest levels of baatezu, Mabrahoring is rarely actually used but for the most formal occasions.
- Least Baatorian
- Though in the same family as Baatorian, Yugoloth is believed to have split from that language at least 500 millennia ago; while the yugoloths maintain it was originally their language, even if this is true, the more flexible nature of the yugoloths somewhat guaranteed its drift from Baatorian. However, it is still largely mutually intelligible with Baatorian, and of course it still holds many of the same characteristics. Most prominently, the multifaceted layers of communication; unlike their use in that language, though, in Yugoloth they are most commonly used to disguise intent from outsiders. Different castes apply different twists of meaning and interpretation, meaning even though the language is largely the same over the entire species, the same utterance from a mezzoloth and a yagnoloth can mean two (or more likely, five or six) entirely different things. No mortal has ever mastered Yugoloth at a level above that of a nycaloth, and it's unlikely any ever will.
- Planar Trade? (Common)
- Tanar'ric (Abyssal)
- Commonly believed to have originally descended from the language of the osyluth, Tanar'ric is spoken differently by every caste of tanar'ri (when it's spoken at all), with only partial mutual comprehensibility from caste to caste. While most make an effort to learn the specific dialects of at least the highest castes of tanar'ri, the balors, marilith, and nalfeshnee, beyond that speech between castes is more a matter of just untangling what one can and taking one's best guess at the intended meaning. The specific dialect most commonly meant when one refers to "Abyssal" is in particular the balor dialect, with the dialects of other castes specified when intended: rutterkin Abyssal, chasme Abyssal, etc.
- Tanar'ric had no written form until after the beginnings of the Blood War, at which point they stole the alphabet of Baatorian, distorting it and using it for their own purposes. The Tanar'ric alphabet today holds little-to-no resemblance to the Baatorian alphabet, though the fact still leads the baatezu to seethe.
- Faces of Evil - The Fiends, pgs.35,55,77
- Fiendish Codex II - Tyrants of the Nine Hells, pg.28
- In the Cage, pg.58