some ungettext strings do not appear in po file if the same string was in an ugettext call elsewhere in the code

[ygbo]

I can only reproduce this issue in a big project (hence ​https://github.com/openstack/horizon/ ) and not in a single file code, so checking out the patch-set 8 of my branch: ​https://review.openstack.org/#/c/91338/ is best to reproduce the issue:

git fetch https://review.openstack.org/openstack/horizon refs/changes/38/91338/8 && git checkout FETCH_HEAD

If you look in horizon/openstack_dashboard/dashboards/project/instances/tables.py line 97 there is a call to return ungettext_lazy(u"Instance", u"Instances", count)

now go in the horizon/openstack_dashboard directory and launch:

python ../manage.py makemessages -l fr

check horizon/openstack_dashboard/locale/fr/LC_MESSAGES/django.po, msgid_plural "Instances" never appears anywhere.
However, msgid "Instances" appears in the pot file, but not as a plural.
The issue is not higly noticible for French, but it is for languages which handle 3,4,5 or 6 plural forms:
​http://docs.translatehouse.org/projects/localization-guide/en/latest/l10n/pluralforms.html?id=l10n/pluralforms

If I try Irish:

python ../manage.py makemessages -l ga

I'm supposed to have 5 plural forms and expect to find in horizon/openstack_dashboard/locale/ga/LC_MESSAGES/django.po:

msgid "Instance"                                                      
msgid_plural "Instances"                                              
msgstr[0] ""                                                                    
msgstr[1] ""                                                                    
msgstr[2] ""                                                                    
msgstr[3] ""                                                                    
msgstr[4] ""

But this appears nowhere so this will not be properly translated.

[Claude Paroz]

Duplicate of #17375