WAV-I bring this up with slight bit of trepidation, but the fact is that "Lingua Franca" was not Latin, nor was it even a full blown language--it has been described as the original "pidgin", and seems to have consisted of words borrowed chiefly from the Romance languages, mostly Italian or possibly Catalan/Provencal/Occitan, with a simple grammar that was apparently drawn from Arabic.

The term "lingua franca" is a metaphorical usage, and is used to describe languages that to function in as an overarching language--but for the most part, these are full scale languages capable of expressing the full range of human experience-