There are several hotels near CDG, including a Sheraton right in Terminal 2 (which is a collection of separate buildings; it isn't in one of the buildings that planes leave from).

That said, unless you'll get in very late or have to leave very early, I'd go into town. There's a train station under the Sheraton for T2, and one that serves T1 but is actually in T3 (a short shuttle bus ride from T1). The ticket agents are used to dealing with tourists. Even if the one you get doesn't speak English, which is unlikely but possible, they know how to communicate - and there ought to be at least one English-speaking agent on duty at all times, with a British flag next to his or her window. (You won't be able to use the automated ticket machines unless you have a credit card with a chip.) There's frequent train service until nearly midnight. The trip takes about half an hour and costs, when last checked, just under 10€ (about US$15). Get a ticket, go to the platforms and stand on the one for the RER B line that says "Direction - Paris." There are several stops in Paris; the one you want will depend on where your hotel is and/or what you want to do before you go there.

Coming back, trains start running at about 5 am. If you'll be traveling during the morning rush hour, keep in mind that Paris commuter rail can be quite hectic then, with boarding involving a certain amount of shoving. Allow plenty of time, and only get on a train if the CDG stations are lit up on the overhead signboards at the platform (hard to describe, but also hard to miss when you're there) since not all northbound RER B trains serve CDG.