They are training them and teaching them how the UK and French air force intends to fight, so essentially they are teaching the Chinese about tactics the western airforces might use against China in any conflict.
Learning how different potential enemies might fight you is valuable... a sort of Top Gun school for them to practise.
A Chinese pilots who has practised against other Chinese pilots might be good, but one who has practised against French and UK pilots and also Russian pilots in exercises gets a broader understanding of air combat and would be better equipped to deal with different enemies because he has practised against more than one "enemy" (not that Russia is an enemy but the west are bound to be eventually...).
Learning how different potential enemies might fight you is valuable... a sort of Top Gun school for them to practise.
A Chinese pilots who has practised against other Chinese pilots might be good, but one who has practised against French and UK pilots and also Russian pilots in exercises gets a broader understanding of air combat and would be better equipped to deal with different enemies because he has practised against more than one "enemy" (not that Russia is an enemy but the west are bound to be eventually...).