It's true that most people leave the defaults. However, there may an easy solution for a subset of cases.
Do the browser defaults in any country include multiple language settings? It seems likely that in most countries, the default would be only one language. And if this is the case, then if multiple alternatives are present in the request headers, it's very likely the user or computer admin has deliberately changed it, and that in turn would mean that sites should respect the choices.
This might still be wrong in when the settings were made by someone other than the current user, or there are multiple languages default-configured, but it might be a step in the right direction.
Do the browser defaults in any country include multiple language settings? It seems likely that in most countries, the default would be only one language. And if this is the case, then if multiple alternatives are present in the request headers, it's very likely the user or computer admin has deliberately changed it, and that in turn would mean that sites should respect the choices.
This might still be wrong in when the settings were made by someone other than the current user, or there are multiple languages default-configured, but it might be a step in the right direction.