> Did you compile international/mule-cmds.el (which was modified by the
> patch)

Yes.

> and did you re-dump Emacs after byte-compiling mule-cmds.el?

I don't know.  This is exactly what I did:
1. I applied your patch to my branch (the whole patch, which includes
the file you mention).
2. To make sure that the patch was correctly applied, I compared your
patch with the output of "bzr diff" (I'm attaching this output if you
want to check it).
3. I went to the "nt" subdirectory and ran a plain "mingw32-make".  I
thought that the build system would know what to recompile based on
what files have changed since the last time.
4. I ran a "mingw32-make install".

> If you did all that, what is the value you get by evaluating
> (terminal-coding-system)

cp1252

>, and what is the value you get from
> w32-get-console-codepage?

"w32-get-console-codepage" is void as a variable.
"(w32-get-console-codepage)" returns 850.

-- 
Dani Moncayo