There is dialogue in French but it was generally used for the initial scenes in part 1 when characters like Frank and Tanya were introduced and when Nodame and Chiaki first arrived in Paris. After that, all the dialogue reverted back to Japanese.
I've watched both parts and I enjoyed it very much although I'd say that I'm inclined to pick part 2 as the better of the two. This special shows the professional growth of Nodame and Chiaki in their music pursuits as well as their relationship as a couple after they come to Paris. There are fewer comic moments here since Masumi, the main source of it together with Nodame, is in Japan and the two new characters introduced - Tanya and Frank play rather small, inconsequential roles. Part 2 is my favourite with the whole array of moods and emotions it swept me up in, particularly with the music pieces used and Nodame's journey of self-discovery which I found very moving. And, of course, there's the change in Chiaki's behaviour towards Nodame from brusque to ... ... oh well he still shies from calling her his girlfriend.
Viewership ratings:
Part 1 - 18.9%
Part 2 - 21.0%