A domain’s default language setting automatically applies to any mailboxes created within that domain, unless you specify a different language for a particular mailbox. Any company- or domain-level administrator can change the default language setting for a domain.
To set the default language
1. Log in to the Mail Administration Console (MAC).
For more information, see "What is the MAC?"
2. Navigate to the domain that you want to modify.
See “Searching in the Mail Administration Console (MAC)”.
3. In the Defaults For New Users section, from the Language drop-down list, select the default language for this domain.
4. Click Update.