Thank you for feedback, Martin. I've amended the the patch.

Next, I've prepared some initial test.support.check__all__ helper, based on generalization of all previous patches. Its name/params' descriptions may be a bit rough - amendments/suggestions for such will be strongly appreciated: Issue23883_support_check__all__.patch

I've added missing test.test_gettext.MiscTestCase, based on aforementioned check__all__ helper: Issue23883_test_gettext.patch 

I've also took the liberty of working on some more modules. These are: csv (using new helper), enum, ftplib, logging, optparse, pickletools, threading and wave: Issue23883_all.patch

ftplib and threading have more functions (missing in their __all__ variables) that appear to be documented than mentioned in msg240217 - namely:
* ftplib.error_temp https://docs.python.org/3/library/ftplib.html#ftplib.error_temp
* ftplib.error_proto https://docs.python.org/3/library/ftplib.html#ftplib.error_proto
* threading.main_thread https://docs.python.org/3/library/threading.html#threading.main_thread

so I've added them as well.