How can we hard code the language of the OWA interface?

The first time a user logs on to OWA the names of the Inbox, Calendar, Contacts and other default folders are localized using the "Accept-Language" header. For example, if the browser language is German the first time the user logs on to OWA then the default folder names will be in German no matter if the browser language is change in future sessions. The language can be hardcoded from the server-side by creating an ISAPI filter in IIS. The filter intercepts all requests and updates the "Accept-Language" value before Exchange receives it.

For more details on this configuration refer to https://support.microsoft.com/kb/310599/en-us.