I suggest you go to the Les Cars Air France desk and tell them where you're going. They have 2-3 coach lines to the centre of Paris and will be able to tell you (in English!) exactly how to get to your hotel after deboarding. You can also get the Roissybus to Opera.
Even if your hotel is not very near these places, a taxi within the city centre won't cost you more than €10-12 (it'll be over €50 if you opt for one from Roissy at night).
The above solution isn't any good if you're arriving after 23:00.