The European version of Tomodachi Life makes me a big deal out of it that you can mix and mash Miis with various different languages. Sadly, this won't be the case for North America. Reader cyberboz contacted a local Nintendo rep and the response was sadly not the one he hoped for. We have translated response here for you below:
''Thank you for contacting us. Unfortunately, I can confirm the information that you have already found out: the North American version of Tomodachi Life will not be available in French at the time of its release.
I can definitely understand your opinion and I want you to know how much we appreciate that you have shared it with us.''