I used to do mock Oxbridge interviews, and I think the people who have the edge over others are the ones who clearly study the subject out of real enthusiasm for it, and who can show a genuine interest in the subject outside of their experience of it at school. So, does your student have anything to show for that? Have they taken an interest in the country they're studying? Have they travelled there, or are they planning to travel there? Do they take an interest in the current affairs or in the literature/history of the country? Have they ever read a novel from that country, listened to a pop song from that country, communicated with someone on a forum etc etc etc? One of the girls I interviewed was planning to do spend a year out doing charity work in the target country (and she'd already been there, I think), and another one was in touch with lots of people from 'his' chosen country over the internet and knew all about its popular music bands - both of these got in.