The other week coming back from LYS (to LHR) the lady checking boarding passes and passports at the gate asked me if I spoke English as I was seated in the exit row (I have an Italian passport) - seems sometimes they check but not always.
What surprised me more was after boarding was completed, I looked across the aisle to find the other emergency exit row having only one person in it sitting in the aisle seat - I thought someone had to sit by the door? (It was later filled by someone who nabbed himself a bit of extra legroom but that's beside the point).