The Lord of the Rings: Shadow of the East
Also called Morlam in Sindarin, Black Speech rose as the language of the Dark Lord’s court in the later Second Age. With Sauron’s fall and the collapse of his empire, Morlam virtually disappeared, a foul tongue spoken only by evil spirits gnawing away at their pain in remote, shadowed places. However, the surviving followers of the dark cults still spoke to these spirits and preserved a few tomes and scrolls written in the forbidden tongue.
After long centuries, the rise of the Witch-king in Angmar allowed the hidden lore to be brought forth and the servants of Darkness to use the Black Speech freely, if only within the bounds of his fortresses. It would be the Witch-king’s ambition to conduct all business in Morlam, but practicality dictates that he tolerate, even at court, the multiplicity of tongues spoken by his many subjects. While the Black Speech is still outlawed in Arthedain, a few loremasters have learned its uncouth cadences so they may better divine the thoughts of their enemies.