For the curious, these are the things that are said in French, in the order they appear. I tried to do it with footnotes and it got very long and confusing.
Hermione: Hi, Harry!
Not too well! I have an Arithmancy test this morning, and I have to study a lot to pass!
What's the matter, Harry?
Thanks, Harry, but it's okay. Really.
Ron: No, I don't think so... I don't know of any. Why?
Alright, mate? (really awkward one, sorry!)
Yes, I can understand you, Harry.
Hermione: Harry, are you sure you're alright?
No, it's perfect English... you think that I'm speaking French?
Hermione: Yes, say that again, please.
Everything we say is in French?
Ron: Breathe, Hermione. Harry- how long have you been hearing French?
That was my question!
Hermione: I know, Ron, but Harry didn't understand it when you asked.
Terry Boot: You coming, Hermione? The test?
Hermione: Oh no! I'm really sorry, Harry, but I've got to go now! If I miss this test I'll fail the class!
Ron: But, Hermione, Harry's problem isn't-
Hermione: Later, Ron! Bye!
. .. ... .. .
Draco: Hello (most people knew that one, though, right? "Bonjour?")
Something longer, more complex... Sorry, sorry. Why did you ask me to speak French?
I said 'better,' and before, 'okay.'
. .. ... .. .
Draco: (everything is the same as above, and then we get) You don't understand English? Really?
I love you. I love you a lot.