I was at DLP for two days - this past May 27 and May 28, by myself, and I'm from the US. I too was very worried about the whole language issue and the "rudeness" issue.
I know very very little French, but noticed if I greeted any castmember with Bonjour, they would launch into French. If I greeted them with Hello, they would launch into English. Even if I tried to finish a conversation with Merci, they always responded in English (You're Welcome, Have a nice Day, etc.). And they were all very pleasant. Sometimes when I started with Bonjour and then in French asked a basic question like "how much" or some such, the castmember would say (in English) do you prefer French or English (guess my accent was atrocious!
I did not run into one castmember either day at either park that could not speak passable English - I'm sure there may be some, but I did not have any trouble at all.
Most of the shows either have English presenations (check the time guides), or have headphones for English (like Honey I Shrunk the Audience). It was weird using the headphones though because you could still hear the French in the back ground and at times it was hard to separate the two and understand (at least for me!!!). But I watched the Lion King presenation in French and was delighted when the songs were all sung in English even though the rest of the production was in French. I knew the story line though so could follow along anyway - and part of what I wanted to experience was the differences between DLP and WDW in Florida where I visit twice yearly.
Now, I did run into a few "rude" guests and definitely a large number who spoke no English.
I must have been very fortunate

but language was NOT my problem!