Verified. Methododology:

1. Copied test_localise.py from the PR into a master checkout.
2. Added a null locale.localize.
3. Verified that all new tests failed.

.. code-block::

  Ran 64 tests in 0.023s

  FAILED (errors=4, skipped=4)
  (base) blockhead:cpython sholden$ vi Lib/locale.py
  (base) blockhead:cpython sholden$ ./python.exe -m test.test_locale
  ...................ssss....F...................testing with ('tr_TR', 'ISO8859-9') .....testing with 'en_US.UTF-8'... .testing with 'en_US.UTF-8'... .testing with 'en_US.UTF-8'... .testing with 'en_US.UTF-8'... .testing with 'en_US.UTF-8'... .testing with 'en_US.UTF-8'... .testing with 'en_US.UTF-8'... .testing with 'en_US.UTF-8'... ....F
  ======================================================================
  FAIL: test_localize_invalid_format (__main__.TestEnUSLocalize)
  ----------------------------------------------------------------------
  Traceback (most recent call last):
    File "/Users/sholden/cpython/Lib/test/test_locale.py", line 613, in test_localize_invalid_format
      locale.localize('foo')
  AssertionError: ValueError not raised

  ======================================================================
  FAIL: test_localize (__main__.TestfrFRLocalize)
  ----------------------------------------------------------------------
  Traceback (most recent call last):
    File "/Users/sholden/cpython/Lib/test/test_locale.py", line 625, in test_localize
      self._test_localize('50000.00', '50000,00')
    File "/Users/sholden/cpython/Lib/test/test_locale.py", line 601, in _test_localize
      self.assertEqual(locale.localize(value, grouping=grouping), out)
  AssertionError: '50000.00' != '50000,00'
  - 50000.00
  ?      ^
  + 50000,00
  ?      ^


  ----------------------------------------------------------------------
  Ran 64 tests in 0.024s

  FAILED (failures=2, skipped=4)

4. Checked out cedk/locale_format branch.
5. Observed that all locale tests now pass.

Seems to me like this one should be good to go, so I've changed the stage to "commit review" and await the application of some core developer's commit bit.