Why was Justinian I known as a Latin-speaking Byzantine emperor?

Justinian I was known as a Latin-speaking emperor primarily because he was an Illyrian of peasant stock for whom Latin was his native language.1

His identity as a Latin speaker was deeply tied to his role as a restorer of Roman tradition and authority. During his reign, he sought to position himself as the pattern of a Roman and Christian emperor, possessing a profound knowledge of Roman history and antiquities. This commitment to his Roman heritage was reflected in his major legislative achievement, the Code of Justinian, which was compiled under his sponsorship. Latin served as the official language for the vast majority of these legal works, including the Codex Constitutionum, the Digesta, and the Institutiones, reinforcing the connection between his administration and the classical Roman legal tradition.23

While he was a cultivated gentleman and a significant figure in the Byzantine Empire, it was noted that he spoke Greek—the primary language of his administration and empire—with a distinct accent, further highlighting his Latin-speaking roots.14