If you see the following error while installing pip:

Traceback (most recent call last):
     File "/usr/bin/pip", line 11, in <module>
       sys.exit(main())
     File "/usr/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 581, in setlocale
       return _setlocale(category, locale)
   locale.Error: unsupported locale setting

this means the environment variable LC_ALL is missing or invalid somehow.

FIX :

run the following command:

export LC_ALL=C

and retry installing again.

What is LC_ALL?

LC_ALL is the environment variable that overrides the value of the LANG and the values of any other LC_* environment variables.

In a script, if you want to force a specific setting, as you don't know what settings the user has forced, your safest and generally only option is to force LC_ALL.

The C locale is for computers. In the C locale, characters are single bytes, the charset is ASCII, the sorting order is based on the byte values, the language is usually US English.
You generally run a command with LC_ALL=C to avoid the user's settings to interfere with your script. For example, if you want [a-z] to match the 26 ASCII characters from a to z, you have to set LC_ALL=C.

Hope this helps! :)