You have to translate the English text to Franch. Download the dictionary Voice from Wojpen. When opened with Notepad or simular programm You see lines with English text and behind the text ="". You have to put the French Translation between the "".
When you have finished the job after a few weeks you can do the folowing:

2) Open your French TTS Voice file witn Winrar 3.93 or below (It wil not work with later versions)
3) Doubleclick on "i18n"
4) Inthere you see "dictionary.voice". Leave the screen open.
5) Just drag the "dictionary.voice" from your translated file to the opened winrar screen. It will overwrite the file in your voice.
6) Close Winrar and you can use voice with updated Dictionary.