how to translate my text to french

If you are asking how to translate from one language into another, Adobe Captivate doesn't do that for you. Your best option is to find a company to perform translation services to translate your text from one language into another. Once translated you could use the Neospeech speech agent for use with French language to generate that text into narration for you. The speech agent you need for French is named Chloe. It would be recommended to have a native French speaker review the final audio to ensure that pauses are placed where necessary.

Don't use Google to translate your narration. Your French audience will spot the poor translation or worse, not understand the narration. Google translate continues to improve but it doesn't already deal with regional differences and it can get grammar wrong. 

If you are using an English version of Captivate, you'll get English voices...

If you have a French version of Captivate you'll get French voices.