Comment 3 for bug 690270

This is really strange, the string seems to be translated in /usr/share/polkit-1/actions/org.debian.apt.policy (at least in Natty):

    <message>To install or remove software, you need to authenticate.</message>
    [...]
    <message xml:lang="zh_TW">若要安裝或移除軟體，您需要通過認證。</message>

Perhaps an encoding problem?

Cheng-Chia Tseng, what happens if you manually modify the /usr/share/polkit-1/actions/org.debian.apt.policy file and translate the "<message xml:lang="zh_TW">" line to something else? (you might need to log out of the session and log back in for the new translation to be loaded)