In French, Window > Secondary Display > Loupe - Live has invalid keyboard shortcuts defined in TranslatedStrings_Lr_fr_FR.txt:
"$$$/MultiMonitor/LiveLoupeShortcut/Mac=Maj+Z"
"$$$/MultiMonitor/LiveLoupeShortcut/Win=Maj+Z"
Localized versions of key modifiers ("Maj") aren't allowed in shortcut definitions. Those lines should be:
"$$$/MultiMonitor/LiveLoupeShortcut/Mac=Shift+z"
"$$$/MultiMonitor/LiveLoupeShortcut/Win=Shift+z"
(Note the lower-case "z".)
Tested on LR 12.0.