What has worked for me is getting up, standing right next to them with a huge smile on my face and asking in a friendly, chatty way - using hand signals to overcome language barriers - for them to turn it down. I smile non-stop, laugh, say sorry, say please, excuse me and maintain nonstop eye-contact, but DO NOT leave until they comply (even if it gets uncomfortable). Has so far worked 100% of the time and overcomes any language barrier (although I have not, and probably would not try, with openly belligerent or drunk passengers).