Playing this game in French changes the timing of conversations. Let's use the opening conversation as an example. For reference, I talked about the English timing here.
In English, Nancy's options are "That's right. Are you Emily's guardian?" and "Emily told me your name. It's...". In French, Nancy's options are "Exact. Vous etes la tutrice d'Emily?" and "Emily m'a dit votre nom. C'est...". As you can see, they're basically the same. The time difference is likely to be negligible.
There are five points, where you pick what Nancy says. In both English and French, it's faster to pick the second option, in points 1, 2, 4 and 5. With 1 and 4, the second option is faster, because Jane's response is shorter. With 2 and 5, the second option is faster, because Nancy says fewer words.
Interestingly enough, the third point where you pick Nancy's response is different in French! In English, you want to pick the option "Is she all right?". That's faster than the second option, where Nancy says, "Maybe she's just...you know, still thinking about her mom." In English, Nancy pauses while saying this line. In French, Nancy doesn't pause. So the second option is faster in French!
It's not THAT much faster. It's .07 seconds faster to pick the second option, if you're playing in French. It's 0.4 seconds faster, to pick the first option, if you're playing in English. So the time difference between the two languages is about 0.5 seconds, for this particular conversation option.
Still, it's interesting how one conversation option is faster in French, and the other is faster in English.
I timed the entire conversation in both languages, following the fastest conversation route. Overall, there is a 3.22 second difference between the two versions. French is faster.