Fixing locale issues

If you get errors when installing packages regarding locale, e.g.

locale: Cannot set LC_CTYPE to default locale: No such file or directory
locale: Cannot set LC_MESSAGES to default locale: No such file or directory
locale: Cannot set LC_ALL to default locale: No such file or directory

Or issues with Python PIP e.g. when trying to use Certbot like

Creating virtual environment...
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/virtualenv.py", line 2363, in <module>
    main()
  File "/usr/lib/python3/dist-packages/virtualenv.py", line 719, in main
    symlink=options.symlink)
  File "/usr/lib/python3/dist-packages/virtualenv.py", line 988, in create_environment
    download=download,
  File "/usr/lib/python3/dist-packages/virtualenv.py", line 918, in install_wheel
    call_subprocess(cmd, show_stdout=False, extra_env=env, stdin=SCRIPT)
  File "/usr/lib/python3/dist-packages/virtualenv.py", line 812, in call_subprocess
    % (cmd_desc, proc.returncode))

Then you may need to install and/or set your locale files. You can check by running

localectl list-locales

and if the output is just something like

C.UTF-8

Then as root do

apt-get install language-pack-en*
   update-locale LANG=en_GB.UTF-8 LC_MESSAGES=POSIX

Your preferred locale name may vary