i18n Python scripts: declare plural forms for Catalan and Slovak
Regarding Slovak language, there was enough info in
<https://code.qt.io/cgit/qt/qttools.git/tree/src/linguist/shared/numerus.cpp>.
As for Catalan, I don't see anything there, so I put
"ca": ["singular", "plural"] based on the fact that [1] says:
"Catalan has an inflectional grammar. Nouns have two genders
(masculine, feminine), and two numbers (singular, plural)."
I suspect we'll be ahead of Qt Linguist for Catalan.
[1] https://en.wikipedia.org/wiki/Catalan_language
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