Ubuntu – How to Change Locale Lang setting in Ubuntu 12.04

locale command should be . LANG=en_US.UTF-8.

My setting are .

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

local file config

   cat /etc/default/locale : 
   LANG="en_US.UTF-8"
   LANGUAGE="en_US:en"

   cat /etc/locale.conf
   LANG="en_US.UTF-8"

What I have already done.

sudo locale-gen en_US.UTF-8 : 
Generating locales...
en_US.UTF-8... up-to-date
Generation complete.

sudo dpkg-reconfigure locales
Generating locales...
  en_IN.UTF-8... done
  en_US.UTF-8... up-to-date
Generation complete.

Please Let me know if you need any thing.

I am not sure /etc/default/locale file is default or custom.