Corpus Juris Civilis was a collection of laws and legal guidelines issued by the Byzantine state from 529 to 534.
There is much content of significance in the Corpus Juris Civilis, including the establishment of Christianity as the state religion of Byzantium. (At least one provision declared anyone who didn't practice officially sanctioned Christianity to be a non-citizen.)
From the language aficionado’s perspective, however, what is significant about Corpus Juris Civilis is that it was the last major state document published in Latin by the Byzantine Empire.
Within a century or two, Latin would fall into disuse in Byzantium, both as a common language, as well as the language of officialdom.
The Byzantine Empire, which long outlasted Latin-speaking Rome, was to be a Greek-speaking, distinctly eastern state.
Although the Byzantine Empire began as a division of Rome, by 600 or so it was no longer wholly Roman in character—at least in terms of language.