I logged in gnome-shell, and found that the display language is set to some strange asian language (I think) without my prompt. I tried to change the locale settings but found that the default language is English (how?) despite of that strange language.

Here's a snapshot, See the strange word instead of "Activity":

I'm on Ubuntu 12.04 LTS.

Output of locale:

LANG=zh_CN.UTF-8
LANGUAGE=zh_CN:en_US:en
LC_CTYPE="zh_CN.UTF-8"
LC_NUMERIC=en_US.UTF-8
LC_TIME=en_US.UTF-8
LC_COLLATE="zh_CN.UTF-8"
LC_MONETARY=en_US.UTF-8
LC_MESSAGES="zh_CN.UTF-8"
LC_PAPER=en_US.UTF-8
LC_NAME=en_US.UTF-8
LC_ADDRESS=en_US.UTF-8
LC_TELEPHONE=en_US.UTF-8
LC_MEASUREMENT=en_US.UTF-8
LC_IDENTIFICATION=en_US.UTF-8
LC_ALL=

Output of locale -a:

C
C.UTF-8
de_CH.utf8
en_AG
en_AG.utf8
en_AU.utf8
en_BW.utf8
en_CA.utf8
en_DK.utf8
en_GB.utf8
en_IE.utf8
en_IN
en_IN.utf8
en_NG
en_NG.utf8
en_NZ.utf8
en_PH.utf8
en_SG.utf8
en_US.utf8
en_ZA.utf8
en_ZM
en_ZM.utf8
en_ZW.utf8
POSIX
zh_CN.utf8
zh_SG.utf8

Solved: This answer did it.