Hi tanin82,
Re: With Spoken Content feature, is it possible to use the same language of a different region?
Am no expert in this area, so may not know what you need, yet your request certainly deserves some response.
At least we get your discussion underway, and others with more expertise may contribute their experience.
Re: My phone is set to French France
Wondering which setting for French France you mean:
✽ Your setting may be the language set for "over-all" use : Settings > General > Language & Region.
More info: Change the language and region on iPhone - Apple Support
or
✽ Just the language you have chosen for Spoken Content : Settings > Accessibility > Spoken Content > Voices: (where you choose a voice and dialect).
It may make a difference whether you use Spoken Content, or VoiceOver, and may depend upon what you want spoken. Eg: used in app(s) like Safari etc., or third-party (non-Apple) app(s), or for reading documents generally.
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More info:
VoiceOver is Apple's gesture-based screen reader: VoiceOver uses the same language you choose for your iPhone. To choose a different primary language, go to Settings > General > Language & Region, then tap Add Language. Languages supported by VoiceOver - Apple Support includes the three French voices you mentioned.
Adjust voice and speed for VoiceOver and Speak Screen on your iPhone, iPad, or iPod touch - Apple Support
Eg: says:
"Your iOS or iPadOS device uses a compact voice for VoiceOver, Speak Screen, and Speak Selection.
But you have a few other options for the voices you can use for speech.
Adjust VoiceOver voices : Enhanced-quality voices can be 100 MB or larger.
Connect your device to Wi-Fi to download and install one of these voices.
With VoiceOver, you can turn on more than one voice, switch between Default and Enhanced Quality (without needing to download the voice again), and change the speaking rate for each voice."
There is more info. (eg: on downloading voices) in the above article.
All the best :-)