The Latin translator would have a real problem. In English it is already contradictory, as it says in English that it is in French. In Latin the problem is even more acute, as the statement in the sentence would have to deny, in Latin, that it is in Latin.
There is actually a Latin translation of Descartes’ book. It is by Etienne de Courcelles and was published in 1644. Descartes himself worked with the translator.
How did they solve the problem of the contradictory statement? They left the sentence out. It was untranslatable in Latin.
Deconstructionists, and Derrida in particular, have focused on various kinds of untranslatability, including the ‘institutional untranslatability’ displayed in the example above. Derrida’s most extensive reflection on this particular example is in the opening chapters of his Eyes of the University. Right to Philosophy 2, trans. Jan Plug et al., Stanford: Stanford University Press, 2004, p. 1-42 (the French original dates from 1990).