Update 2015-05-12: Seems the correct file to edit is /etc/default/locale:

export LANGUAGE="en_US.UTF-8"
echo 'LANGUAGE="en_US.UTF-8"' >> /etc/default/locale
echo 'LC_ALL="en_US.UTF-8"' >> /etc/default/locale

Then reboot.

I’m really digging dokku-alt. Dokku is a simple way of setting up a deployment setup as easy as Heroku’s. Dokku-alt is that plus some bundled plugins.

I had some troubles though with the Postgresql databases being created with ASCII encodings. So before you install and setup dokku get your locales in order - make your /etc/locales look like:

LANG=en_US.utf-8
LANGUAGE=en_US.utf-8
LC_CTYPE="en_US.utf-8"
LC_NUMERIC="en_US.utf-8"
LC_TIME="en_US.utf-8"
LC_COLLATE="en_US.utf-8"
LC_MONETARY="en_US.utf-8"
LC_MESSAGES="en_US.utf-8"
LC_PAPER="en_US.utf-8"
LC_NAME="en_US.utf-8"
LC_ADDRESS="en_US.utf-8"
LC_TELEPHONE="en_US.utf-8"
LC_MEASUREMENT="en_US.utf-8"
LC_IDENTIFICATION="en_US.utf-8"
LC_ALL=en_US.utf-8

Source it (or reboot) and then set up dokku.