Ever since the government of England had been taken over by a Norman elite with the conquest of 1066, French had been the language of the court, of government and of education. English was still spoken by the common people throughout this period, of course, but from approximately 1350, it also started to be used again for literary texts. The second half of the fourteenth century saw a flowering of literature in Middle English that included the anonymous Sir Gawain and the Green Knight, William Langland's Piers Plowman, and the works of Geoffrey Chaucer.
Editors. "English replaces French as educational language". The Literary Encyclopedia. First published 31 July 2012
[http://www.litencyc.com/php/stopics.php?rec=true&UID=9459, accessed 26 February 2017.]