Validate msgid_plural against msgstr[0] for languages with nplurals=1

[tomasr8]

The python format checker currently only validates msgid against the translation for languages with only one plural form. msgid_plural is not checked. For example, this:

msgid "foo"
msgid_plural "foo %s"
msgstr[0] "bar"

does not get flagged even though it should (missing %s in the translation).

Here's a real-world example:

#, python-format
msgid ""
"There is currently <strong><a href=\"%(url)s\">one active API "
"key</a></strong> in the system."
msgid_plural ""
"There are currently <strong><a href=\"%(url)s\">%(count)s active API "
"keys</a></strong> in the system."
msgstr[0] "系统中当前有 <strong> <a href=\"%(url)s\"> %(count)s 个活动 API 密钥 </a> </strong>。"

This translation should get flagged if it was missing the %(count)s placeholder since it appears in msgid_plural. it's not the case because only msgid is checked currently.

(This translation actually produces warnings as is, because the singular does not contain %(count)s, so perhaps an even better solution would be to only validate against the plural, but I'm not so sure about that)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.69%. Comparing base (2b93a4a) to head (b38f7f0).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1198   +/-   ##
=======================================
  Coverage   91.69%   91.69%           
=======================================
  Files          27       27           
  Lines        4694     4696    +2     
=======================================
+ Hits         4304     4306    +2     
  Misses        390      390           

Flag	Coverage Δ
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macos-14-3.11	90.67% <100.00%> (+<0.01%)	⬆️
macos-14-3.12	90.88% <100.00%> (+<0.01%)	⬆️
macos-14-3.13	90.88% <100.00%> (+<0.01%)	⬆️
macos-14-3.8	90.60% <100.00%> (+<0.01%)	⬆️
macos-14-3.9	90.66% <100.00%> (+<0.01%)	⬆️
macos-14-pypy3.10	90.73% <100.00%> (+<0.01%)	⬆️
ubuntu-24.04-3.10	90.75% <100.00%> (+<0.01%)	⬆️
ubuntu-24.04-3.11	90.69% <100.00%> (+<0.01%)	⬆️
ubuntu-24.04-3.12	90.90% <100.00%> (+<0.01%)	⬆️
ubuntu-24.04-3.13	90.90% <100.00%> (+<0.01%)	⬆️
ubuntu-24.04-3.8	90.62% <100.00%> (+<0.01%)	⬆️
ubuntu-24.04-3.9	90.68% <100.00%> (+<0.01%)	⬆️
ubuntu-24.04-pypy3.10	90.54% <100.00%> (+<0.01%)	⬆️
windows-2022-3.10	90.74% <100.00%> (+<0.01%)	⬆️
windows-2022-3.11	90.68% <100.00%> (+<0.01%)	⬆️
windows-2022-3.12	90.89% <100.00%> (+<0.01%)	⬆️
windows-2022-3.13	90.89% <100.00%> (+<0.01%)	⬆️
windows-2022-3.8	90.72% <100.00%> (+<0.01%)	⬆️
windows-2022-3.9	90.67% <100.00%> (+<0.01%)	⬆️
windows-2022-pypy3.10	90.74% <100.00%> (+<0.01%)	⬆️

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