When a user logs in, we store their current language in a cookie, so we can display non-signed in screens in that language after they log out
In case the cookie is not there (e.g. a person accesses Willow for the first time), we fall back to the browser language for Sign In and Forgotten Password screens (if supported, English language otherwise)
We fallback to the organisation language for Set Password and Download Files screens if the user doesn't exist