Bug: user guide compile failed.

[ytetsuro]

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Describe the bug
user guide compile failed.

CodeIgniter 4 version
develop

Affected module(s)
none

Expected behavior, and steps to reproduce if appropriate

I want write document for CodeIgniter4, but ocurr error following.

$ cp -p Vagrant.dist Vagrant
$ vagrant up
$ vagrant ssh
vagrant@ubuntu-bionic:~$ sudo easy_install "sphinx==1.4.5"
vagrant@ubuntu-bionic:~$ sudo easy_install sphinxcontrib-phpdomain
vagrant@ubuntu-bionic:~$ cd codeigniter/user_guide_src/cilexer
vagrant@ubuntu-bionic:~/codeigniter/user_guide_src/cilexer$ sudo python setup.py install 
vagrant@ubuntu-bionic:~/codeigniter/user_guide_src$ cd ../
vagrant@ubuntu-bionic:~/codeigniter/user_guide_src$ make html
sphinx-build -b html -d build/doctrees   source build/html
Running Sphinx v1.4.5
Exception occurred:
  File "/usr/local/lib/python2.7/dist-packages/Sphinx-1.4.5-py2.7.egg/sphinx/locale/__init__.py", line 195, in _
    return translators['sphinx'].ugettext(message)
KeyError: 'sphinx'
The full traceback has been saved in /tmp/sphinx-err-9eCUXz.log, if you want to report the issue to the developers.
Please also report this if it was a user error, so that a better error message can be provided next time.
A bug report can be filed in the tracker at https://github.com/sphinx-doc/sphinx/issues. Thanks!
Makefile:40: recipe for target 'html' failed
make: *** [html] Error 1
vagrant@ubuntu-bionic:~/codeigniter/user_guide_src$ cat /tmp/sphinx-err-9eCUXz.log
# Sphinx version: 1.4.5
# Python version: 2.7.17 (CPython)
# Docutils version: 0.16 release
# Jinja2 version: 2.10.3
# Last messages:
# Loaded extensions:
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/Sphinx-1.4.5-py2.7.egg/sphinx/cmdline.py", line 243, in main
    opts.warningiserror, opts.tags, opts.verbosity, opts.jobs)
  File "/usr/local/lib/python2.7/dist-packages/Sphinx-1.4.5-py2.7.egg/sphinx/application.py", line 163, in __init__
    self.setup_extension(extension)
  File "/usr/local/lib/python2.7/dist-packages/Sphinx-1.4.5-py2.7.egg/sphinx/application.py", line 473, in setup_extension
    mod = __import__(extension, None, None, ['setup'])
  File "/usr/local/lib/python2.7/dist-packages/sphinxcontrib/phpdomain.py", line 109, in <module>
    class PhpObject(ObjectDescription):
  File "/usr/local/lib/python2.7/dist-packages/sphinxcontrib/phpdomain.py", line 119, in PhpObject
    TypedField('parameter', label=_('Parameters'),
  File "/usr/local/lib/python2.7/dist-packages/Sphinx-1.4.5-py2.7.egg/sphinx/locale/__init__.py", line 195, in _
    return translators['sphinx'].ugettext(message)
KeyError: 'sphinx'

Context

• OS: Ubuntu
• Web server none
• PHP version none