In the fourteenth and fifteenth centuries, England inherited a very complex and shifting linguistic situation. While English continued its slow and uneven ascent to political and literary prominence, French retained its important presence. Numerous manuscripts of Walter de Bibbesworth’s Tretiz de langage (also called Femina) appeared throughout the fourteenth and the fifteenth centuries. Twenty copies of guides to French letter-writing, or collections of sample letters, were also produced during the same centuries. Such works illustrate the continuing practical uses of Anglo-French in the later Middle Ages in England. This article examines multilingualism on the page—occasions and usually specific written spaces where contextually unexpected languages suddenly, even dramatically, appear. It considers languages of authenticity, which shift considerably in varied settings from the twelfth to the fifteenth centuries, and the broad move from authenticating French to authenticating Latin.