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. 2 Three developmental stages as viewed from a multilingual perspective Prior to the fifteenth century, Londoners (and people elsewhere in Britain) kept accounts not in monolingual English, but in either a Medieval Latin or Anglo-Norman French matrix, with English (and sporadic words from other languages) embedded in a syntactically orderly manner. Certain linguistic elements were particularly resistant to representation in Medieval Latin or Anglo-Norman. Names of people, their social ranks and titles, place-names, currencies weights and measures, and the names of specific traded commodities were likely to be retained in their original form. Nouns and deverbal-ing forms could, noncategorically, appear in English. Illustration is given with some extracts from the London merchant and moneylender Gilbert Maghfeld's account-book for the years 1372-1395. The main matrix language (that is, the syntactic framework) is Anglo-Norman: