Mac: set-language-environment trashes default-file-name-coding-system

[Benjamin Riefenstahl]

Hi all,

- Start Emacs as emacs -q. 
- default-file-name-coding-system is set to 'utf-8. 
- M-x set-language-environment RET UTF-8 RET. 
- default-file-name-coding-system is now set to 'iso-latin-1 (!). 

On Mac OS X the encoding of filenames is always UTF-8.

The problem occurs in the implementation of set-language-environment
in mule-cmds.el.  set-language-environment calls
reset-language-environment which sets default-file-name-coding-system
to iso-latin-1 unconditionally.  After that, set-language-environment
calls set-default-coding-systems but that function avoids setting
default-file-name-coding-system specifically on Darwin/Mac OS X.

benny