multilingual vs polylingual

multilingual

adj

  • Of, relating to, or involving multiple languages. 

  • able to communicate in a number of languages. 

noun

  • a polyglot 

polylingual

adj

  • of or pertaining to multiple languages; multilingual 

  • able to use multiple languages 

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