Dungeons & Dragons
Infernal is the language of the baatezu, a subtype of devils. Infernal was brought to Toril through contact with evil beings from other planes. It is described as beautiful, yet alien in nature, since it developed among beings with thought patterns very unlike those of humanity. Clerics often take the time to learn it, and the Infernal alphabet is used to transcribe the Thayan dialect of the Mulhorandi language.
Castes of Speech
The Infernal tongue is tied closely to the baatezu caste system, being divided into four parts. Though each part uses the same basic foundation, each expresses different concepts and uses different words.3
The tongue of the least baatezu, such as the spined devils, is a simple, harsh tongue suited for shouting commands across a battlefield.
The tongue of the lesser baatezu is equal to any mortal tongue in complexity, used to communicate abstract concepts such as honor or hate. It is less gravelly than the tongue of the lesser baatezu, though not exactly musical. Most non-devils who learn Infernal learn this variation of it.
The stilted, formal, grating yet strangely melodic tongue of the greater baatezu is full of obscure patterns that seem to meander misleadingly before snapping to an unexpected point.
Speaking it properly requires careful planning and the ability to respond intelligently to phrases based only on the most subtle of cues. It’s said that two greater baatezu can hold entire conversations in this form of Infernal using only the beginnings of their sentences. It is nearly impossible for mortals to learn.
The fourth form of Infernal is the court language of Baator, used only by pit fiends and the archdevils. This form of the language is so utterly corrupt and evil that its malevolence can drag listeners into hateful despair just through hearing its patterns.