They should disappear after issuing:

sudo locale-gen en_US en_US.UTF-8
sudo dpkg-reconfigure locales
dpkg-reconfigure reconfigures packages after they have already been installed. Pass it the names of a package or packages to reconfigure. It will ask configuration questions, much like when the package was first installed.

sudo locale-gen en_US en_US.UTF-8
sudo locale-gen en_GB en_US.UTF-8
sudo dpkg-reconfigure locales

Just add the following to your .bashrc file (assuming you're using bash)

export LC_ALL="en_US.UTF-8"