>
> > file-name-coding-system
> > utf-8-nfd
>
> Where is that defined?
>

In ns-win.el


Can you try using utf-8-hfs?  (You might need to load ucs-normalize
> first.)
>

It behaves like the original, as far as I can tell.

I tried setting it to nil. This made completion work. However, the letters
are presented in decomposed form, so that pressing backspace first converts
"å" to "a", a second backspace deletes the "a" -- this is not how we would
like to present file names to users.

    -- Anders