​What does Destination mailbox language set?

Answer:

Destination mailbox language sets the language for system folder names in Outlook Web Access (OWA), but only in the case where a user or admin has never previously logged in to the mailbox.

To further explain this, here are examples:

• If the account has been created at the Destination but no one has ever logged into the account, then whatever language is set within MigrationWiz Advanced Options via this Destination mailbox language setting will be the language that OWA interface is set to. Note: It will not perform any translation on actual mailbox content.
• If the account has been logged in to prior to migration, this MigrationWiz Advanced Option setting will not have any effect. This setting only effects mailboxes that have never been logged in to, before migration. For example, if the user logs in to OWA and sets their OWA language to German, but the MigrationWiz Advanced Option language setting is set to French, the OWA interface language will remain set as German.

Note: If a user wants to manually set their own language in OWA, KB004355 explains the steps to do this.