The word in french is a compound, anyway, so it doesn't pluralize in the regular way.
From the en.wikipedia.org
British newspapers do indeed compare things to Wales, but they never pluralize the noun.
From the economist.com
In the Ilokano language, CV-reduplication is used to pluralize nouns.
From the en.wikipedia.org
How do you properly pluralize terms that are phrases?
From the scienceblogs.com
Also, some nouns pluralize by way of Umlaut, and some undergo no pluralizing change in certain cases.
From the en.wikipedia.org
Damn the Liberals, they had one chance, and one chance only, to break the duopoly and to pluralize politics.
From the guardian.co.uk
It is rare to pluralize furniture in this way.
From the en.wikipedia.org
The internal plural employs vowel quality or apophony to pluralize words, similar to English man vs. men and goose vs. geese.
From the en.wikipedia.org
We must pluralize that term.
From the blogs.psychcentral.com
More examples
Mark with a grammatical morpheme that indicates plural; "How do speakers pluralize nouns in Japanese?"
(pluralization) the act of pluralizing or attributing plurality to
To make plural
(pluralization) A feature of ActiveRecord that generates much controversy. Models have singular names, like person, while views and controllers use plurals of those names, because they work with many instances of the models. ...