I have successfully released my app on the App Store but the language displayed in the App information is English despite the fact that I have selected French as the primary language for my app when I submitted it.
Any idea how to display French in the language section of the App Store ?
You have to provide French localization for your app to have French included as your app's languages. Open the project Info page in Xcode, and double check the Localization settings.
It should show something like: Base, English, French, etc... in the list. If French is not in there, add it, and write the text translations manually in .strings file for example.
The languages that you add (or set as primary) on App Store Connect while submitting the app for review is only usable for setting localized App Store app descriptions, promotional texts, tags, or screenshots for different languages. It's basically for advertising purposes only.