mm-find-mime-charset-region

mm-find-mime-charset-region is a compiled Lisp function in `mm-util.el'.

(mm-find-mime-charset-region B E &optional HACK-CHARSETS)

Return the MIME charsets needed to encode the region between B and E.
nil means ASCII, a single-element list represents an appropriate MIME
charset, and a longer list means no appropriate charset.