[i18n] I change horde to use native language, but it does not take effect

[???]

Hi all,

	I have a problem that when I change horde's language support, but it does not take effect.

For example, at this login web page: http://X.X.X.X/horde/ , I change "Language" to non-English language, but the words

do not change at all. They are still English.

	I have set $nls['defaults']['language'] to 'zh_TW' and I am using 

OS:debian Sarge

Horde 3.1.1
PHP 4.4.2
MySQL 4.1.13
Apache 2.2.0

How can I realize this scene: when I change the language at login web page http://X.X.X.X/horde/, it changes accordingly.

I have googled the web, but no fortune.

Any help are appreciated!