pip install - locale.Error: unsupported locale setting

Run the following command (it will work):

export LC_ALL="en_US.UTF-8"
export LC_CTYPE="en_US.UTF-8"
sudo dpkg-reconfigure locales

The root cause is: your environment variable LC_ALL is missing or invalid somehow

Short answer-

just run the following command:

$ export LC_ALL=C

If you keep getting the error in new terminal windows, add it at the bottom of your .bashrc file.

Long answer-

Here is my locale settings:

$ locale
LANG=en_US.UTF-8
LANGUAGE=
LC_CTYPE="C"
LC_NUMERIC="C"
LC_TIME="C"
LC_COLLATE="C"
LC_MONETARY="C"
LC_MESSAGES="C"
LC_PAPER="C"
LC_NAME="C"
LC_ADDRESS="C"
LC_TELEPHONE="C"
LC_MEASUREMENT="C"
LC_IDENTIFICATION="C"
LC_ALL=C

Python2.7

    $ uname -a
    Linux debian 3.16.0-4-amd64 #1 SMP Debian 3.16.7-ckt11-1+deb8u6 (2015-11-09) x86_64 GNU/Linux
    $ python --version
    Python 2.7.9
    $ pip --version
    pip 8.1.1 from /usr/local/lib/python2.7/dist-packages (python 2.7)
    $ unset LC_ALL
    $ pip install virtualenv
    Traceback (most recent call last):
      File "/usr/local/bin/pip", line 11, in <module>
        sys.exit(main())
      File "/usr/local/lib/python2.7/dist-packages/pip/__init__.py", line 215, in main
        locale.setlocale(locale.LC_ALL, '')
      File "/usr/lib/python2.7/locale.py", line 579, in setlocale
        return _setlocale(category, locale)
    locale.Error: unsupported locale setting
    $ export LC_ALL=C
    $ pip install virtualenv
    Requirement already satisfied (use --upgrade to upgrade): virtualenv in /usr/local/lib/python2.7/dist-packages