Among the studies flourished in the field of historical sociolinguistics, mainly in the strand devoted to English history, during its medieval and early modern phases, multilingual texts have been analysed using theories and models coming from contact linguistics, thus applying synchronic models and approaches to the study of the past. This contribution aims at investigating the role and the usage of the languages in the Johnsons’ correspondence in the XVI century. Their letters display interesting usages of Anglo-Norman, Latin, and French in different ways; therefore, the present study will scrutinise the above-mentioned documents, trying to explore the nature of the non-native elements, whether they are formulaic and inherited or they can be considered idiosyncratic forms of code switching. After analysing the letters and the type of multilingualism in them, I will also attempt to evaluate the functions given to the French language in specific contexts.