Python locale error: unsupported locale setting.md

• Refference: http://stackoverflow.com/a/36257050/3445802

user@dev:~$ sudo 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
user@dev:~$ sudo su
root@dev:/home/user# export LC_ALL="en_US.UTF-8"
root@dev:/home/user# export LC_CTYPE="en_US.UTF-8"
root@dev:/home/user# pip install virtualenv
Collecting virtualenv
  Downloading virtualenv-15.0.1-py2.py3-none-any.whl (1.8MB)
    100% |████████████████████████████████| 1.8MB 533kB/s 
Installing collected packages: virtualenv
Successfully installed virtualenv-15.0.1

why though? Everyone say's how to fix it.. I've used Python/pip for a decade and only today on a production system that has worked fine is this error showing up? Any thoughts on WHY it just randomly happened?