If it's a debian image, you can add the following in your Dockerfile
RUN apt-get install -y locales locales-allENV LC_ALL en_US.UTF-8ENV LANG en_US.UTF-8ENV LANGUAGE en_US.UTF-8
try:
export LANGUAGE=en_US.UTF-8export LC_ALL=en_US.UTF-8export LANG=en_US.UTF-8export LC_TYPE=en_US.UTF-8sudo locale-gensudo dpkg-reconfigure locales
Normally you can install other locales with:
sudo locale-gen en_USsudo locale-gen en_US.UTF-8sudo update-locale
then you can change the values in /etc/default/locale.
/etc/default/locale