For the Windows defined properties, such as Title, Tags, etc., that message is provided by Windows itself, so using the Windows defined language. For the PDF-ShellTools specific, and custom defined, properties, that message is provided by the PDF-ShellTools defined language.
Some PDF-ShellTools interface localization files are not full updated to the last version, such as the French, so I supposed that's why you don't see that message localized in your chosen language. To fix it, you just need to add that entry to the French.lng file, and reset the selected PDF-ShellTools interface language, using the manager.