1. The problem
  2. The fix

Tired of warning about locales in Ubuntu? Me too, and there is a fix.

The problem

You login, you try to compile something, etc. All the time you see this:

perl: warning: Setting locale failed.   
perl: warning: Please check that your locale settings:   
        LANGUAGE = "en_US:en",   
        LC_ALL = (unset),   
        LC_MESSAGES = "en_US.UTF-8",   
        LANG = "en_US.UTF-8"   
    are supported and installed on your system.   

The fix

Edit the file /etc/environment and add this:

LC_ALL=en_US.UTF-8
LANG=en_US.UTF-8

If it still fails, add the same lines to /etc/default/locale.