>>> "Eli" == Eli Zaretskii <eliz@gnu.org> writes:

   >> From: Uwe Brauer <oub@mat.ucm.es>
   >> Cc: Uwe Brauer <oub@mat.ucm.es>, emacs-devel@gnu.org
   >> Date: Fri, 16 Nov 2018 17:00:40 +0100
   >> 
   >> >> 2. Is there any faster possibility?
   >> 
   >> > Faster than what?
   >> 
   >> Then typing 
   >> C-x RET c mac-roman RET C-x C-f FILE-NAME RET
   >> 
   >> I mean open the file, mark the region and recode the text to the correct
   >> coding. 

   > If you already have the file visited in Emacs, then

   >   C-x RET r mac-roman RET

   > will revert the buffer with that encoding.  Is this what you wanted?

But still wondering why 

(decode-coding-region (region-beginning) (region-end) 'mac-roman)

Does not work.