Planar Tongues

Planespeak
There is a common language spoken across the multiverse which has evolved from smatterings of various planar languages. This language is called PlaneSpeak. Its use has been spread by merchants, rogues, adventurers and faction members all around the multiverse. Since this language is meant to be used by different peoples and races, it cannot convey complex thoughts. For the same reason, this language comprises only simple sounds, ie base vowels (a e i o u) and consonants (sounds like ts, dz, x, zh, pt are not used). The main areas of use for PlaneSpeak are: Sigil (it is the native language); the Outlands (native language or trade language); the first layer of each outer plane, since it is the most visited layer (used as a trade language) PlaneSpeak is much less widely spoken on the less accessible layers of the outer planes, on the Inner Planes, and on the Prime (each prime world tends to have its own common).However, since the Clueless do understand PlaneSpeak a little, sages speculate that the various prime commons might be related to PlaneSpeak.

Koine Sophias
Since PlaneSpeak cannot convey complex thoughts, an erudite language used by priests, factols, wizards, bureaucrats etc. in Sigil has developed with time.This scholarly language is called Koine Sophias, or simply Sophias. It is used for most publications, for official notices, and to debate in the Hall. Sophias is almost only spoken in Sigil among educated people. However, it is also used in those burgs or realms devoted to knowledge gods, such as Thot’s realm in the Outlands.

The Trade Tongue Of Law
The petitioners in Arcadia love tending their fields; they also like to travel through the agreeable Arcadian countryside and to visit fellow Arcadians (‘tis an easy way to keep an eye on what one’s neighbour’s up to).

Unfortunately, although petitioners forget their previous life, they tend to still speak the language they used to speak when they were ‘alive’. This proved unpractical to Arcadians, who spoke (among other tongues) Egyptian, Sumerian, Toril prime common, dwarvish, etc.

An Arcadian common tongue grew from the need to communicate with each other, and this common tongue became the standard language in Arcadia, supplanting any other language there.

Dwarven war parties, hardhead adventurers, diplomats, and merchants eventually brought the use of this tongue to Acheron, to Mount Celestia, to the first layer of Baator, and to lawful gate towns in the Outlands. The Arcadian common tongue has thus become to be known and used as the Trade Tongue of Law.

Guvners, Mercykillers and Hardheads are known to sometimes use it in Sigil, hence the false belief in the existence of Faction Languages.

Aegyptos
Aegyptos is the language of the Children of Ptah. Al’malamut, Osirion, Hamunaptra, Mulhorrand, and all other ancient cultures worshipping the Aegyptian Pantheon speak a form of this language. It’s written form is hieroglyphs. It is spoken across the Planes and on many PRime worlds as well.

Hellenic
The Greek Pantheon is a close-knit one. Although most Greek powers make their home on Arborea, many others reside in other planes, and despite alignment differences, they like to stay in touch.

The endless travels of ambassadors, messengers, spies, and even petitioners between the various Greek realms has lead to the establishment of a common language in all these realms.
This language is called Hellenic.

Since it is a precise and rich language, it has been picked up as a common language for diplomacy in many outer planes.

Also, beings speaking Hellenic are often found on Mount Olympus, the River Oceanus, and the Styx. Hellenic has thus also become a useful trade tongue on these planar pathways.
The numerous Greek-sounding names for planes and layers attest the diffusion of Hellenic on the Outer Planes.

Lower Planar Trade
A language developed by the Yuggoloths to help facilitate trading between Baatezu and Tanar’ri. It consists of a blend of Abyssal and Infernal and is known for having some of the most passionate and precise profanity of any planar tongue

Legalspeak
Legalspeak may be taken as a bonus language by any starting Guvner. If the Guvner has no bonus languages (or joins after character creation), it may be taken for the cost of a single skill rank, regardless of the Guvner’s class. Legalspeak is obtuse and impenetrable for non-speakers, combining Draconic with The Trade Tongue of Law (but either root language is hardly recognizable as a part of Legalspeak), as well as over a millennium of Guvner jargon and professional terms.

Midani
On a remote prime world called Toril, there is a remote continent of enlightened people who know how to properly address Genies, and who respect them. Genies have hence come to like these people and to visit their land with pleasure, and they have come to adopt their language as a useful tool to communicate with mortals. This language is called Midani.
Midani is spoken in the Inner Planes and on those Outer Planes where one can find enlightened petitioners.

The Myth of Faction Languages
A blood can find many bashers in Sigil who’d swear Faction Languages do exist, extremely twisted versions of the Cant that members of each faction use amongst themselves. As noted in paragraph C above, this is only a legend, based on the fact that poor sods hearing high-ups speaking in Sophias or hardheads using the Trade Tongue of Law got really confused.
Fact is, only factotums, factors and factols would be interested in such a language. Namers do have other business to mind than their faction’s and they’d lack the time or the will to learn a language of so limited a use.