I posted an extensive trip report of my trip to DLP last month in this section. Feel free to read for more info, but I'll give a few responses to your questions here...
Language
All signage that you would need to understand, and all safety spiels are in French and English (and sometimes others). Indeed, many of the attraction signs (for example, Main Street and Frontierland) are English-first, French second. Cast members speak both French and English, so, for exmaple, ordering food was not a problem at all. On-ride narration, etc. is generally in both French and English, but a variety of techniques are used. I discuss many of them in my trip report, but I'll give a few examples below. Know, however, that the fact that I only speak English was a non-issue. Didn't stop us or even slow us down in any respect.
Animagique, Cinemagique, Lights Moteurs Action, the daytime parade, and some other show-type attractions feature characters/CMs speaking English and French in turn, but the script ensures that all can understand.
Playhouse Disney and Stitch Live have shows in different languages at different times.
Rides with speaking roles, like PoTC, Star Tours, Snow White, etc. had some characters speaking French and some English. It impacted some understanding (for example, I don't know if the auctioneer in PoTC actually said "Show 'em your larboard side"), but not the point where the actraction was seriously difficult to follow.
Some segments of pre-shows, etc. had French narration with English subtitles or vice-versa. Again, no problem figuring out what was happening.
Eating
I can only provide my experiences. If you stay in a hotel near DLP, breakfast in your hotel will be included. At the parks, be prepared for sticker shock, as everything in expenses (moreso than WDW). We ate at the Agrabah Cafe, Plaza Gardens, and Walt's. All were of comparable quality to buffets/table-service at WDW, and I wouldn't hestitate to go back. One nice thing was that I made reservations only a week before the trip and had no trouble getting what I wanted. Of course, I didn't want any character meals, which I understand are extremely popular there.
Not to be Missed
I'm assuming you are an experienced visitor to WDW in the US, and a Disney nut like most of us here. Taking that into account, here are my "Not-to-Missed-Attractions". I'm not including on the list DLP attractions that are very much like their US versions (Star Tours, Buzz, etc.). I'm assuming you already know whether you want to ride those. Where I have included attractions that have a US version, it's because the DLP version is different/unique/better.
Big Thunder Mountain
Phantom Manor
Swiss Family Treehouse
Adventure Isle
Storybookland Boats
Castle Walkthrough
Space Mountain
Fantillusion parade (if it is still running)
Alice's Curious Labyrinth
Animagique
Cinemagique
Armageddon
Crush's Coaster
As for the when to do them, I don't have enough experience to know the traffic patterns. In a 2 1/2 day trip, however, making normal use of fastpasses, etc., I had no trouble doing all of these and most everything else in both parks.