The Shantiri Empire was a technologically advanced civilization which predated all current nations of Ashan and which collapsed for unclear reasons.
Mythology[]
From the Spirit world, the Dragon Gods send visions to their mortal servants, instructing them in proper worship. This leads to the foundation of the Shantiri Empire which unifies all six Elder races into a single nation. The Shantiris spread across the face of the world, building titanic cities and temples. But the conflict between Angels and Faceless tore the empire apart and each of the elder races founded their own kingdoms. Soon after, the Primordial Twins of Urgash and Asha became myth and legend.
Language[]
The Shantiri Empire used their own language. There is not much known about it. For example the word "Khar" means "skull" in the Shantiri language.
Speculation[]
Since the Shantiri Empire was much more technologically advanced than any current nation of Ashan and assuming the Ancient universe and Ubisoft continuity are one and the same, it might actually have been part of the Empire of the Ancients which collapsed in the Silence when communications were disrupted between colonies of the interplanetary empire. Ashan's inhabitants would have eventually forgotten their actual origins and created their own mythologies, similar to the inhabitants of other colonies like Enroth, VARN-4, and Xeen before the interplanetary chase between two Ancient Guardians named Sheltem and Corak revealed the actual origins of each world whereas Ashan's inhabitants have remained in isolation as they have not interacted with any other world yet.
Moreover, since Ashan's history is based on the Mage Sar-Elam the Seventh Dragon instead of the Silence as other Ancient colonies, then it is difficult to compare them as they are not based on the same event.
Assuming the Shantiri Empire was actually the Ashan colony of the Empire of the Ancients, then its language might have been a local colonial language as the other known Ancient colonies didn't share the same language.