ACCEPT_LANGUAGE goes before default_langauge

See https://github.com/nextcloud/server/issues/970

Before we had

1. Users settings in personal settings
2. Admins default language settings
3. Accept-Language settings of the browser

However this is not in line with
https://www.w3.org/International/questions/qa-lang-priorities

So this changes the order to

1. Users settings in personal settings
3. Accept-Language settings of the browser
2. Admins default language settings