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.

So:

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!)

Of course!

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?

Ron: What?

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!

Darn it!

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?

Okay... Better?

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.