lect vs lingua franca

lect

noun
  • A specific form of a language or language cluster: a language or a dialect. 

lingua franca

noun
  • A common language used by people of diverse backgrounds to communicate with one another, often a basic form of speech with simplified grammar, particularly, one not the first language of any of its speakers. 

How often have the words lect and lingua franca occurred in a corpus of books? (source: Google Ngram Viewer )