[1] The language is spoken by the inhabitants of the “northern continents” of the future earth, the Ascians, who are enslaved by their masters (the Group of Seventeen) in a way much like the people of Oceania in George Orwell's book 1984.
Although unfamiliar to most readers, this is not a word invented by Wolfe, nor is it a form of "Asians"; rather, it means 'dweller of the tropics', and it came into English by way of medieval Latin as an adaptation of ancient Greek ἄσκιος, literally 'without a shadow'.
[2][3] In the tropics, the sun is exactly overhead at noon twice a year, and at that time a person standing straight up will cast no shadow.
As the northern continents are at war with the southern Commonwealth (where most protagonists of the books live), there are interpreters in the Ascian army to interrogate prisoners.
In "The Citadel of the Autarch", the fourth volume of The Book of the New Sun series, there is a story told by an Ascian prisoner (who identifies himself only as "Loyal to the Group of Seventeen"), which is translated by people of the Commonwealth into our way of speaking.