How to configure locales to Unicode in a Docker Ubuntu 14.04 container?

I use this in my Dockerfile:

# Set the locale
RUN locale-gen en_US.UTF-8  
ENV LANG en_US.UTF-8  
ENV LANGUAGE en_US:en  
ENV LC_ALL en_US.UTF-8

One can also use the ENV one-liner:

RUN locale-gen en_US.UTF-8
ENV LANG='en_US.UTF-8' LANGUAGE='en_US:en' LC_ALL='en_US.UTF-8'

The /etc/default/locale file is loaded by PAM; see /etc/pam.d/login for example. However, PAM is not invoked when running a command in a Docker container. To configure the locale, simply set the relevant environment variable in your Dockerfile. Example:

FROM ubuntu:trusty
ENV LANG en_US.UTF-8
CMD ["/bin/bash"]

Try

ENV LANG C.UTF-8

If you get the unsupported locale setting error and don't want to install any new locales.