Update French translation (#3117)

* Update French translation

* Apply suggestions from code review

Co-authored-by: Stanislas Signoud <[email protected]>

* Update src/locale/locales/fr/messages.po

Co-authored-by: Stanislas Signoud <[email protected]>

* Change `étiquette` to `mot-clé`

* Change other usages of `actualité` to `actu`

* Update messages.po

* Change certain space characters to non-breaking spaces

* Update src/locale/locales/fr/messages.po

* Update src/locale/locales/fr/messages.po

Co-authored-by: Stanislas Signoud <[email protected]>

* Update messages.po

* Remove superseded strings and match some

* Add new translations

* Update revision date

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Co-authored-by: Stanislas Signoud <[email protected]>