frankly vs in plain English

frankly

adv
  • To a degree large enough as to be plainly evident. 

  • In a frank or candid manner, especially in a way that may seem too open, excessively honest, or slightly blunt. 

  • In truth, to tell the truth. 

in plain English

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