Trouble with pre-commit script and UTF-8

Hello!

I have trouble with pre-commit hook script:
svn: Can't convert string from native encoding to 'UTF-8'

So I have wrote VERY simple pre-commit script to test this. Here is test
script:

#!/bin/sh
export LANG=ru_RU.UTF-8
date >/dev/stderr
exit 1

As you can see it must be always fail and give me error with current date
text in Russian :-) But it gives me
svn: Can't convert string from native encoding to 'UTF-8'

If I replace
date >/dev/stderr
with
date | hd >/dev/stderr

Then script works as expected end give me hexdump of UTF-8 encoded text.

How can I (if I can) give error messages in pre-commit script in native
language?
post-commit script which mails me list of commited files works like expected
even with files with cyrillic file names.