If like me you just have upgraded your Debian system to Lenny, you probably encounter the following warnings while launching perl:

perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
        LANGUAGE = (unset),
        LC_ALL = (unset),
        LANG = "fr_FR.UTF-8"
    are supported and installed on your system.
perl: warning: Falling back to the standard locale ("C").

To get rid of these annoying messages, I’ve just reconfigured locales with the command:

# dpkg-reconfigure locales

Choose your locale when you’re asked for your “Default locale for the system environment”.

You should have a message like:

Generating locales (this might take a while)...
  en_US.UTF-8... done
Generation complete.

Then, logout, login and your perl installation works fine!