Sitharsis

Sitharsis, also known as simply the Sith language, was the dialect of the Sith species as well as the many governments that the Sith controlled, such as the Sith Dynasty and the Sith Empire.

The language was often used by those who spoke Galactic Basic during rituals, as seen when Darth Dulcia proclaimed a number of acolytes to become apprentices

Appearances
Bright Shadow
 * Chapter 11 (first appearance)