Finds out which languages THIS device can speak and hear. Tap the big button first, then test each language.
If a language says speaking… but you hear nothing: check the volume, and on an iPad check the mute switch in Control Centre.
If it says no voice installed: on a Mac go to System Settings → Accessibility → Spoken Content → System Voice → Manage Voices and download it.
On an iPad or iPhone: Settings → Accessibility → Spoken Content → Voices.