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

I installed a Ubuntu Trusty container using Docker, and when I connect to it, I can see that the locale is set to the bare minimum:

sudo docker run -i -t <id> /bin/bash
root@<id>:/# locale
LANG=
LANGUAGE=
LC_CTYPE="POSIX"
LC_NUMERIC="POSIX"
LC_TIME="POSIX"
LC_COLLATE="POSIX"
LC_MONETARY="POSIX"
LC_MESSAGES="POSIX"
LC_PAPER="POSIX"
LC_NAME="POSIX"
LC_ADDRESS="POSIX"
LC_TELEPHONE="POSIX"
LC_MEASUREMENT="POSIX"
LC_IDENTIFICATION="POSIX"
LC_ALL=

I need to use an Unicode locale (for instance the US English one, en_US.UTF-8).

I tried to edit the /etc/default/locale file and put this inside:

# cat /etc/default/locale 
LANG=en_US.UTF-8

But even after leaving the container and coming back, the locale is still not properly set.

I also tried using the update-locale command, without any success:

root@cab13a6abe4f:/# update-locale LANG=en_US.UTF-8
root@cab13a6abe4f:/# locale
LANG=
LANGUAGE=
LC_CTYPE="POSIX"
LC_NUMERIC="POSIX"
LC_TIME="POSIX"
LC_COLLATE="POSIX"
LC_MONETARY="POSIX"
LC_MESSAGES="POSIX"
LC_PAPER="POSIX"
LC_NAME="POSIX"
LC_ADDRESS="POSIX"
LC_TELEPHONE="POSIX"
LC_MEASUREMENT="POSIX"
LC_IDENTIFICATION="POSIX"
LC_ALL=

On my local configuration, I have the following configuration:

LANG=en_US.UTF-8
LANGUAGE=en_US
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=

How can I have the same in my Docker container?

Thanks in advance!

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.

I tried this and it helped me in Dockerfile after my image I add

ENV LANG='en_GB.UTF-8' LANGUAGE='en_GB:en' LC_ALL='en_GB.UTF-8'
RUN echo en_GB.UTF-8 UTF-8 >> /etc/locale.gen && locale-gen

and run

docker-compose build
docker-compose up -d