How remove unused locale?

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Well, with today disk space, I don't think 0,5Gio is really a big issue...

But, you can define a RPM macro to select the used locale. For example, create a /etc/rpm/macros.lang file (or any other name you want), with

%_install_langs en:fr:fr_FR:fr-FR

Then, during new package installation / upgrade, only selected locale will be installed. This will not affect already installed package.