TAO can be configured for an overall default language as well as a separate language for guests.
To set the default language configuratiop in TAO, you will need to edit generis.conf.php in the config directory where you have installed TAO:
In this file you will be able to configure the default language for the system, as well as the default language that will be used for guests (non-logged in users). For the default language, you will need to update the
DEFAULT_ANONYMOUS_INTERFACE_LANG parameter will set the specified interface language that will be used when no user is currently logged in.
In this example, the system would use English US as the default language for the interface, however guests would be defaulted to Italian. Users would continue to utilize the language they were configured for when created once logged in.