The Chronicles of Etinerra
Demons in Dark Ages are beings connected to the elements of creation. Demons are chaotic in nature, very intelligent. The strongest are very powerful creatures. Elementals are a form of demon, but not as fully developed, lacking a strongly developed free will and self-determination as compared to Demons. It is said that the Demons and Dark Ones form alliances when it suited one party or the other, but they were also just as quick to go to war against each other.
Demons do not “speak” in the normal sense, but communicate by vapors and smoke. A demon will communicate with non-demons by blowing the vapors over the recipient so that they smell (and understand) them. Someone smelling the vapors has a general understanding of what the demon is saying. Those who are trained in the language of demons will have an exact understanding. If a non-demonic being wants to summon a demon, orcommunicate with demons must do so by obtaining expensive hookahs, fine spices and other materials (at least 100gp per HD of demon being communicated with) and using those during the summoning and/or communication to blow smoke/vapors back. Only those trained in the language of demons, or those using a summoning spell, may do this. The smoke/vapors may cross the boundary of a summoning/magickal circle without effect on the circle.