What we have to consider:

 - Userland (POSIX locale) and kernel (locale-like? or UTF8?)
 - Unionfs
 - Symlinks
 - Mountpoints
    (/<Russion dirname>/<Japanese dirname>/<German filename>,
     but this could not be accessible from processes with
     LC_ALL=de_DE.ISO8859-15 for example)
 - Multiple encoding in a single volume
    (which we allow currently; suppose /home for Russians
     and Japanese, and /home on a UFS)
 - Msdosfs, shortnames in legacy encoding and longnames in UCS2
 - something else?

Partly discussed in http://www.haun.org/ml/b-l-j/a/500/572.html
(in Japanese, sorry).

Anyway, I do not think all of the above can be solved in a
single solution:), but it is worth discuss before adding a
mount option to specify encoding.

-- 
Minoura Makoto <minoura@valinux.co.jp>
Engineering Dept., VA Linux Systems Japan