You don't need to know French at all to take the Eurostar. It is fully bi-lingual as is Gare Du Nord where you will arrive in Paris. Then when you leave the station, just take a taxi to where you want to go. This is far, far easier than flying if you are going London city centre to Paris city centre, and it's faster when you consider all the time spent at the airports and travel to the city.
As for Orly, it is closer and a shorter and cheaper taxi ride than CDG. But it really depends on where you are going.