Comment 2 for bug 1452400

I did a little debugging and digging on this. The issue seems to lie in elements/debootstrap/install.d/12-debian-locale-gen

While a call is made to debconf-set-selections to preseed the locale value /etc/locale.gen does not get modified and is effectively empty causing dpkg-reconfigure locales to throw an error. I worked around it by simply appending the desired locale string in there before calling dpkg-reconfigure, ala:

<snip>
locales locales/default_environment_locale select en_US.UTF-8
EOF
echo "en_US.UTF-8 UTF-8" >> /etc/locale.gen # I ADDED THIS
dpkg-reconfigure -f noninteractive locales
|<snip>

After that change to the debootstrap element my Debian images are building.