In Japanese (ja_JP), LR has an incorrect assignment for Library Loupe Zoom Out -- it is currently "Cmd + ," but should be "Cmd + -". Typing "Cmd + ," in Library Loupe opens Preferences.
In Develop, Zoom Out is assigned "Cmd + -" (and it works).
The offending lines in TranslatedStrings_Lr_ja_JP.txt:
"$$$/AgLibrary/Menu/View/ZoomOut/Key=Cmd+,"
"$$$/AgLibrary/Help/Shortcuts/Zoom_out/Key=Command + ,"