Many of our users are confused when Moodle returns to the default question upon next login, after they changed their language via the language dropdown-menu in the navbar.
I think it would help to clear things up and improve accessibility if a link to language preferences was added to the language menu. Also, this would make it similar to the message and notification menus, which also feature direct links to message and notification preferences in Boost.
Another improvement would be to include another string in the preferred language menu to make it clear to users that this changes the default language upon next login, since it is counter-intuitive that you can change your preferred language there and nothing happens.
Or maybe it would be even better to get rid of the "preferred language" setting altogether, and just make the language-dropdown menu change the preferred language as well as the language for the current page? That might be the most straightforward solution...