I've always wondered about this. Realistically, what are the chances of a non-native getting a job for a flag carrier? I.e a Brit with a decent level of French getting on this scheme. Or someone who is French, Spanish, etc with decent enough English getting a job with British Airways? Disregarding dual-citizenship and that sort of thing.
Or is it one of those things where technically "anyone" can apply, but behind closed doors only those who fit in perfectly with the airline's image will be selected? I.e faultlessly accented nationals?
My personal opinion is that if I got on a British Airways flight, I would expect to hear British accents from the crew. The same as I would expect German from Lufthansa, French from Air France, Dutch from KLM, and Australian from Qantas. Nothing to do with racism or discrimination. It's the fitting-in with the brand around the airline. I would be quite disappointed if I got on BA flight and the PA announcements were in broken English with undertones of Spanish, French, German, etc.
I understand there are some smaller flag carriers who probably don't have many nationals to choose from, as well as the likes of Emirates and Etihad who have crew from all over the world, but I've always wondered about what the chances are of a non-national flying for a big flag carrier.