If the code doesn't match what it should be for the localization you would like to use for your slice (or if it uses a generic locale like 'POSIX'), run something like the following commands:

sudo /usr/sbin/locale-gen en_US.UTF-8
sudo /usr/sbin/update-locale LANG=en_US.UTF-8

I should get these two lines tattooed somewhere, as I always end up on google, when setting up some new lucid boxes…