I am the author of Intelligent Speaker - extension for browser, we use the best available speech engine - Polly from Amazon.
You can get your podcast feed and grab m4a files (better than mp3 - better quality for smaller filesize).
You can e.g. use the free Balabolka which can save as MP3. It's free and runs on Windows. It will detect the installed voices.
You'll need a French voice so that the text sounds proper. Using e.g. Microsoft Anna will not give good results. Nuance has French voices for ~ 40 €.