dnn uses its own fall back mechanism, like this:

for first time anonymous users: try to select language that is part of the visitor's preferred language as set up in the browser. ie. if your portal supports en-US and es-MX, and your visitor's browser has es-ES as preferred language, then es-MX will be chosen, whereas, if your portal supports en-US, es-MX and es-ES, es-ES will be chosen. In other words: es-MX will act als culture neutral language for all preferred locale that have es as language component, as long as es-MX is the only available language for spanish visitors.

If the visitor's preferred language is not supported by the portal, then the portal default language will be selected.

Selected languages will be saved in a cookie.

After a user logs on, the preferred language in his profile will become the active language

Cheers,
Erik

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