From the time of the Conquest, England was a trilingual country. French was the language both of court and of the baronage, while French and Latin were used among the literate and educated clerics, Latin being the language of records and documents. English continued to be used by the majority of the population. During the "Barons' War, an English party emerged, resenting non-English favourites at court, and English was used for administrative purposes. However, without French, there was no possibility of advancement, social or political. But during the middle years of the 14c things began to change. John Trevisa said in 1385 'children leave French and learn in English'. The first piece of parliamentary English is a petition of the "mercers to parliament in 1386. English was the first language of Henry IV, who took the throne in 1399. Henry IV's will is the earliest king's will in English since the Conquest. Its first words are, 'I, Henry, sinful wretch'. In turn, Henry V conducted all business in English: he used it in much written correspondence. His letters are also the earliest letters of a monarch in his own hand to survive. A note in the London Brewers' Company's records sets down their future use of the "vernacular, rather than French, following the king's (Henry V's) own use and insistence. They noted that English had begun 'to be honourably enlarged and adorned'. -
Dictionary of Medieval Terms and Phrases. Christopher Coredon with Ann Williams.