Tancred was a Norman from southern Italy. The Normans who settled Italy and Sicily hired Byzantine tutors for their sons, many of whom taught Arabic as well as Greek. Sicily had been an Islamic port for centuries, and the Christians who lived there copied Arab dress and mannerisms. Roger II of Sicily was also fluent in Arabic and even decorated his coronation robes with Arabic script.

To extend the question: How many people spoke more than one language (apart from the church)?