In a word: French
French was the official language of England for almost 400 years. There were many forms of French dialect used in England from 1066 to 1453.
England
I'm going to go with you want to know what the official court language was following the Norman Invasion in 1066 and the time when English became the language in use, in which case it was French.
In the year of 1066
William of Normandy invaded England in 1066
William Duke of Normandy, crowned king of England in Westminster Abbey on Christmas day 1066.
25 December 1066.
Harold Godwinson was the last Anglo-Saxon King of England, who reigned England from January 6, 1066 until his death at the Battle of Hastings on October 14, 1066.
1066
william
In 1066, the comet was seen in England and thought to be an omen.
William was nominated to be king of England. He wasn't chosen so he decided to come over and conquer England and be king. He came over to England in 1066