I'm not sure what you mean by "contradictory information" ;)
This is how the procedure works for new anonymous visitors:
* an attempt is made to get the preferred languages array from the browser.
* in the preferred order of the array, for each language, an attempt is made to match the preferred language to an available enabled language in the portal. Partial matches are ok, so if a preferred language is fr-BE, an the portal offers an available language fr-FR, then fr-FR is selected
Mind you: after the first selection is done, this value is saved in a cookie, which will be used next time to select the language. If a cookie is available, the preffered language in the browser are not taken into account. The presedence order is this: querystring, form, cookie, browser. Mind you: only for unauthenticated users. For authenticated users the language is set to the profile language after manual or automatic logon.
In order for the process for anonymous users to work correctly, you should clear the domain cookies each time you change the browser preference, otherwise, the value of the cookie is used instead.
NB: this procedure works ok in dnn 3.2.2, earlier versions have some bugs in the selection process.
Cheers,
Erik