[derefr]

> Imagine walking up to a computer in a shared space (hotel lobby, library, etc.) and it's been configured to send out accept-language: <something you don't understand>.

If web browsers could somehow figure out they were running either under a guest/public-use account, or in a kiosk mode, they could avoid sending an Accept-Language header at all. Then,

1. in cases where the header is sent, it would mean a lot more (and hopefully override both online-profile-stored and IP-detection-based answers);

and 2. in cases where the header isn't sent, using an answer from an online profile setting or IP-detection would no longer be against-standard.