This paper focuses on three developmental stages in the history of English which are apparent from a multilingual perspective but which are currently omitted from textbooks: the late medieval mixed-language business system, the fifteenth century tip-point when the switchover to English was imminent, and the subsequent shift to Proto-Standard English. I survey recent work which shows a disruption phase in the last few decades of the fourteenth century in both Anglo-Norman and mixed-language writing. Starting with this disruption phase around the 1370s and continuing to the tip-point to monolingual English around the 1480s (the dating is not concrete, it varies from archive to archive, but roughly fits these parameters), I argue that the intervening century constitutes a period of transition from Medieval Latin to Proto-Standard English.