If I understand this correctly, the "Trash" mailbox, for example,
becomes "Papierkorb" in German, but the folder in /Library/Mail/
where its messages are stored is still named "Deleted
Messages.mbox" in English. (?)
That's correct.
If 'mbox' is a reference to a mailbox, then the Mail command ...
name of mbox
always - always - ALWAYS returns the name of a folder located
somewhere within the /Library/Mail/ folder.
This allows me to get exactly what I want -- the path to a folder
of message files. I couldn't care less what the visible mailbox
names are! In other words it is precisely "the names on disk" which
do concern me.