UI / OpenID language selection

This document describes how Trivore Identity Service selects language to use in user-interface when logging in via OpenID Connect.

1. If user is NOT logged in

   1. The languages given in ui_locales parameter are preferred, for example ?ui_locales=fi

   2. If ui_locales is not present, browser locales are used

2. If user is logged in (via “remember me”)

   1. ui_locales parameter is ignored

   2. User’s own language that is stored in user profile is preferred

   3. If user does not have preferred language, browser locales are used.