Same issue here in Italian, system folders names are not translated and there's confusion in Outlook beacause I can find both "inbox" and "Posta ricevuta", "Sent items" and "Posta inviata", "Notes" and "Note" ecc...
Before MAPI can be used, this must be addressed.
Gabriele Maoret - Head of SysAdmins at SERSIS
Currently manages 6 SmarterMail installations (1 in the cloud for SERSIS which provides services to a few hundred third-party email domains + 5 on-premise for customers who prefer to have their mail server in-house)