Date can dish it out, but not parse it back in

[jidanni]

Date can dish it out, but not parse it back in, for other languages:
$ date
五  1月 16 00:49:11 CST 2009
$ date|date -f -
五  1月 16 00:00:00 CST 2009
$ LC_ALL=C date|date -f -
五  1月 16 00:49:26 CST 2009
$ locale
LANG=zh_TW.UTF-8
LC_CTYPE=zh_TW.UTF-8
LC_NUMERIC="zh_TW.UTF-8"
LC_TIME="zh_TW.UTF-8"
LC_COLLATE=C
LC_MONETARY="zh_TW.UTF-8"
LC_MESSAGES=C
LC_PAPER="zh_TW.UTF-8"
LC_NAME="zh_TW.UTF-8"
LC_ADDRESS="zh_TW.UTF-8"
LC_TELEPHONE="zh_TW.UTF-8"
LC_MEASUREMENT="zh_TW.UTF-8"
LC_IDENTIFICATION="zh_TW.UTF-8"
LC_ALL=
$ date --version
date (GNU coreutils) 6.10