Microsoft Outlook cannot change the default folder names using ResetFolderNames

When you:

• connect to a Microsoft Exchange Server 2010 mailbox by using Microsoft Outlook.
• use the English UI in Outlook, so the default folder names (such as Inbox or Sent Items) are displayed in English.
• install a new language pack for Outlook, and then you change the Outlook UI to the new language.
• restart Outlook by running the Outlook.exe /ResetFolderNames command to reset the default folder names to the new language.

then folder names in Outlook are not changed to the new language.

To change language you need to use one of those methods:

In Exchange Management Shell run:

Set-MailboxRegionalConfiguration -id <alias> -LocalizeDefaultFolderName:$true -Language <Language_code_to_switch_to> -DateFormat <your_preferred_DateFormat>

For more information about the possible language codes and the Set-MailboxRegionalConfiguration cmdlet, go to the following MSDN websites:

Language Codes
Set-MailboxRegionalConfiguration

Another Method is to use OWA (Outlook Web App)

1. Log on to Outlook Web App by using your credential.
2. Click Options, and then click See All Options.
3. Click Settings, and then click Regional.
4. On the Regional Settings page, change the language, select the date and time format that you want to use, and then select the Rename default folders so their names match the specified language option.
5. Click Save, and then exit Outlook Web App.
6. Restart Outlook.