sphinx-quickstart fails when $LC_ALL is empty

[cocoatomo]

Subject: sphinx-quickstart fails when $LC_ALL is empty

Problem

• sphinx-quickstart fails when $LC_ALL is empty

Procedure to reproduce the problem

$ python3.7 -m venv venv
$ . venv/bin/activate
(venv) $ pip install sphinx
(venv) $ export LC_ALL=
(venv) $ sphinx-quickstart

Error logs / results

Traceback (most recent call last):
  File "/private/tmp/issue/venv/bin/sphinx-quickstart", line 11, in <module>
    sys.exit(main())
  File "/private/tmp/issue/venv/lib/python3.7/site-packages/sphinx/cmd/quickstart.py", line 616, in main
    locale.setlocale(locale.LC_ALL, '')
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/locale.py", line 604, in setlocale
    return _setlocale(category, locale)
locale.Error: unsupported locale setting

Expected results

sphinx-quickstart do not raise exception

Reproducible project / your project

• Nothing (this issue occurs before having a project created)

Environment info

• OS: macOS 10.14.1
• Python version: 3.7
• Sphinx version: 1.8.2

[ghost]

I don't believe this is a Sphinx bug specifically. The idiom of locale.setlocale(locale.LC_ALL, '') works on Windows/Linux even if LC_ALL is empty. From research it seems to be a problem specific to Mac:

https://bugs.python.org/issue18378#msg215215

[tk0miya]

@remyabel Thank you for comment.

I understand the error has been filed on bugs.python.org. I just made a workaround for the bug at #5829.
I believe it helps users on Mac OS.