Don't take a tour, what a waste of money and time, but, do consider the hop on and off bus, L'Open Tour. You do NOT need french to enjoy Paris. And a one day visit .. well if you can say Bonjour and Merci , you will survive fine.
L'Open Tour has a website, in english. It costs 26 euros for an all day pass, there are four routes the buses circle all day long, and a basic taped audio guide is provided on the bus. You will be able to hop off , take pictures , buy an ice cream and hop back on and keep going, where as on a fully guided bus tour YOU have no choices at all.
Don't be so nervous, Paris is FILLED with english speaking tourists, not just Americans, there are the Australians, the Brits, the Canadians,and the New Zealanders! They all manage fine, in most touristy central areas ( which is where you will be all day ) even the cafes have menus in english.