If it is the English language credit card software triggered by American bank card, perhaps not the restaurant’s fault (or choice)? Doesn’t make sense that tip request would have been on one “hard copy” but not another, right? They would have to be bending themselves into a pretzel to produce that kind of paperwork.
I agree that it’s deceptive when a restaurant asks in whatever way for a tip in Paris, as though the service is not included (e.g. please see my diatribe on treatment at the then-recently starred Nicholas Flamel: Beware Nicholas Flamel--Paris) .
Still, I am an American, alors, and I tend to tip well for good/excellent service no matter what side of the “pond” I am on. I figure that no matter how much the waitstaff salaries are in Paris (the answer to this question I have never quite understood), I cannot imagine that they are so high that tips on top of “service” fee would be out of line. And the service in most of the restaurants I go to in Paris really is quite wonderful. Also, since I often dine alone (and can only therefore be eating and paying for one meal), the “service” percentage is necessarily low for that table (usually for two).
But I agree that it should be a choice and not deceptive!