l10n: refresh the FlightGear-Qt.xlf and FlightGear-nonQt.xlf files

Florent Rougonrequested to merge
frougon/flightgear-fgdata:refresh-translations into release/2024.1

Also complete the French translation and automatically fill the en_US -nonQt translation using fg-update-translation-files's fill-english-translation action.

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