Problem:
When you’re migrating, and you see the new mailbox has standard folders in 2 different languages.
Or
You cannot change the default folder names to another language by using the /ResetFolderNames switch in Outlook
Solution 1
Use Powershell in the local server to correct this:
set-MailboxRegionalConfiguration -id <alias> -LocalizeDefaultFolderName:$true -Language <Language_code_to_switch_to> -DateFormat <your_preferred_DateFormat>
Use these language codes :
http://msdn.microsoft.com/en-us/library/ms533052(v=vs.85).aspx
More info about set-MailboxRegionalConfiguration :
http://msdn.microsoft.com/en-us/subscriptions/dd351103(v=exchg.141).aspx
Solution 2
If you’re not the exchange administrator, or you use Office 365/Exchange Online :
The standard folders are in Dutch AND in English
Login in outlook WebApp, en select Options
Select Settings => Regional Settings => check “Rename default folders so their names match the specified language” => Save
Start outlook and the folders are renamed.
For more information about this problem :