During the eighteenth century, more women than before succeeded in finding a voice of their own and in exercising intellectual or literary authority. Letters proved an ideal environment for them to explore, shape and justify their intellectual and authorial self. Women’s letters gave, moreover, clear evidence of their interest in multilingualism, because early modern women found themselves at the crossroads of languages due to their active participation in transcultural intellectual networks and their contribution to cultural transfers. In this essay we examine to what extent multilingualism served a strategic purpose in the letters of eighteenth-century women writers: how did multilingualism inform their intellectual and authorial identity formation and representation? To that end, we will explore the dynamic interplay between language, gender and intellectual authority, in the letters of Isabelle de Charrière (1740–1805), a Dutch and Swiss woman writer who was raised and educated in the so-called lingua franca of the Republic of Letters. Our analysis sheds new light upon the way in which Enlightenment women writers, such as Charrière, actively (re)shaped their intellectual and authorial identity. It also contributes a fresh perspective to the growing scholarly interest in the transcultural and multilingual dimensions of early modern women’s lives and works.