I would put the presentation into French, for two basic reasons:

 - just to make sure that when you glance at the screen any word triggers a train of thought in French

 - the audience also has the French ppt to look at matching what they hear from you.

I understand that the thesis is in English, but they won't necessarily open that until after depending on the questions - which they have probably already prepared...

Also, anytime I have to listen to one language and read a second (and I have a DUT to go with my BEng Hons) I always change to comparing the errors in expression / translation and loose the real message.

So, go with French ppt & language and BEST OF LUCK - you will be fine.

Autrement dit : Bonne chance Chef !!