I wouldn't know about the Vim equivalent, but I wrote this in my Emacs config long ago:

    (defun find-non-ascii ()
      "Find and show all of the non-ascii characters."
      (interactive)
      (occur "[[:nonascii:]]"))

It has proved quite useful on occasion.

(Yes, I could just invoke Occur directly, but I can never quite remember the regexp character class and syntax here.)