Full stacktrace:

➜  ~ pip install virtualenv
Traceback (most recent call last):
  File "/usr/bin/pip", line 11, in <module>
    sys.exit(main())
  File "/usr/lib/python3.4/site-packages/pip/__init__.py", line 215, in main
    locale.setlocale(locale.LC_ALL, '')
  File "/usr/lib64/python3.4/locale.py", line 592, in setlocale
    return _setlocale(category, locale)
locale.Error: unsupported locale setting

On the same server, I successfully ran pip install virtualenv with python 2.7.x.

Now, I’ve just installed python3.4 using curl https://bootstrap.pypa.io/get-pip.py | python3.4.

➜  ~ pip --version
pip 8.1.1 from /usr/lib/python3.4/site-packages (python 3.4)

pip uninstall virtualenv throws the same error too

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

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

Someone may find it useful. You could put those locale settings in .bashrc file, which usually located in the home directory.
Just add this command in .bashrc:
export LC_ALL=C
then type source .bashrc
Now you don’t need to call this command manually every time, when you connecting via ssh for example.

While you can set the locale exporting an env variable, you will have to do that every time you start a session. Setting a locale this way will solve the problem permanently:

sudo apt-get install locales
sudo locale-gen en_US.UTF-8
sudo echo "LANG=en_US.UTF-8" > /etc/default/locale

[This answer is target on linux platform only]

The first thing you should know is most of the locale config file located path can be get from localedef --help :

$ localedef --help | tail -n 5
System's directory for character maps : /usr/share/i18n/charmaps
                       repertoire maps: /usr/share/i18n/repertoiremaps
                       locale path    : /usr/lib/locale:/usr/share/i18n
For bug reporting instructions, please see:
<https://bugs.launchpad.net/ubuntu/+source/glibc/+bugs>

See the last /usr/share/i18n ? This is where your xx_XX.UTF-8 config file located:

$ ls /usr/share/i18n/locales/zh_*
/usr/share/i18n/locales/zh_CN  /usr/share/i18n/locales/zh_HK  /usr/share/i18n/locales/zh_SG  /usr/share/i18n/locales/zh_TW

Now what ? We need to compile them into archive binary. One of the way, e.g. assume I have /usr/share/i18n/locales/en_LOVE, I can add it into compile list, i.e. /etc/locale-gen file:

$ tail -1 /etc/locale.gen 
en_LOVE.UTF-8 UTF-8

And compile it to binary with sudo locale-gen:

$ sudo locale-gen 
Generating locales (this might take a while)...
  en_AG.UTF-8... done
  en_AU.UTF-8... done
  en_BW.UTF-8... done
  ...
  en_LOVE.UTF-8... done
Generation complete.

And now update the system default locale with desired LANG, LC_ALL …etc with this update-locale:

sudo update-locale LANG=en_LOVE.UTF-8

update-locale actually also means to update this /etc/default/locale file which will source by system on login to setup environment variables:

$ head /etc/default/locale 
#  File generated by update-locale
LANG=en_LOVE.UTF-8
LC_NUMERIC="en_US.UTF-8"
...

But we may not want to reboot to take effect, so we can just source it to environment variable in current shell session:

$ . /etc/default/locale

How about sudo dpkg-reconfigure locales ? If you play around it you will know this command basically act as GUI to simplify the above steps, i.e. Edit /etc/locale.gen -> sudo locale-gen -> sudo update-locale LANG=en_LOVE.UTF-8

For python, as long as /etc/locale.gen contains that locale candidate and locale.gen get compiled, setlocale(category, locale) should work without throws locale.Error: unsupoorted locale setting. You can check the correct string en_US.UTF-8/en_US/....etc to be set in setlocale(), by observing /etc/locale.gen file, and then uncomment and compile it as desired. zh_CN GB2312 without dot in that file means the correct string is zh_CN and zh_CN.GB2312.

For Dockerfile, this works for me:

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  

How to install locale-gen?

docker ubuntu /bin/sh: 1: locale-gen: not found

I had the same problem, and "export LC_ALL=c" didn’t work for me.

Try export LC_ALL="en_US.UTF-8" (it will work).

The error message indicates a problem with the locale setting. To fix this as indicated by other answers you need to modify your locale.

On Mac OS X Sierra I found that the best way to do this was to modify the ~/bash_profile file as follows:

export LANG="en_US.UTF-8"
export LC_ALL="en_US.UTF-8"
export LC_CTYPE="en_US.UTF-8"

This change will not be immediately evident in your current cli session unless you reload the bash profile by using: source ~/.bash_profile.

This answer is pretty close to answers that I’ve posted to other non-identical, non-duplicate questions (i.e. not related to pipenv) but which happen to require the same solution.

To the moderator: With respect; my previous answer got deleted for this reason but I feel that was a bit silly because really this answer applies almost whenever the error is “problem with locale”… but there are a number of differing situations, languages, and environments which could trigger that error.

Thus it A) doesn’t make sense to mark the questions as duplicates and B) doesn’t make sense to tailor the answer either because the fix is very simple, is the same in each case and does not benefit from ornamentation.

Ubuntu:

$ sudo vi /etc/default/locale

Add below setting at the end of file.

LC_ALL = en_US.UTF-8