This paper will argue that the version of French developed by the authors of thirteenth- and fourteenth-century encyclopaedias is in itself a locus of translingual encounter. Gathering ‘all knowledge’, as encyclopaedias purport do, entails engaging with a network of citations, authorities and languages. Much source material is of course in Latin, and French encyclopaedias vary in their tactics for translating Latin: can Latin words simply be absorbed and naturalized into French, or must they be retained in Latin and marked as somehow foreign and untranslatable? And beyond Latin, other languages and cultures hover into view: Arabic and Greek authors and sources are frequently cited, and words from those tongues at times appear untranslated in encyclopaedic French. Cataloguing the animal, vegetable and mineral world leads to entities located in India and Persia, with other nomenclatures thus entering the picture. A complex set of rhetorical operations is used to deal with non-Francophone words, ideas and voices: the diversity of material that is integrated into the encyclopaedia stands as testament to its completeness, but signalling that diversity hints at the particularity and limits of the French language that is serving as its receptacle. This leads to questions about the shifting function and status of French in the period: as it becomes a more authoritative vehicle for knowledge, does French become somehow more open and plural, and less anchored to France or even to Latinate cultures? Encyclopaedic French was a undoubtedly a key vehicle for the spread of the language – encyclopaedias were widely disseminated texts – but they suggest that French became a boundary-crossing language precisely by allowing in non-Francophone cultures.