Proto-Csillan is the ancestor of language family spoken by the Čis ('tʃis)- a humanoid blue-skinned race inhabiting the planet in the Unknown Regions- the most famous of which is Grand Admiral Ťran (θran). Proto-Csillan was spoken circa 24,000 BBY, waaaay before the Čis developed spaceflight technology. Note Zahn used spellings Cheunh, Chiss and Thrawn in place of Csillan, Čis and Ťran. In-world linguists cannot even begin to hope to reconstruct as far as this language (imagine, like, 10,000 years before PIE, so it spawned a super-family, not just a family), I'm just using this as a base to derive the descendants (which will equate more or less to PIE and will be reconstructed.)