To override this problem you can do that from powershell on Exchange server:
Set-MailboxRegionalConfiguration -identity
Otherwise you need to go to:
OWA -> Options -> Settings -> region and here in addition to select the language you put the flag in the option Rename default folders with a name that matches the language specified.
[original article http://sistarelli.com/2015/06/06/rinominare-le-cartelle-predefinite-di-exchange-2013/]