Spoken audio uses a voice installed on your own device. Install your language once, then tap 🔊 Speak again:
iPhone / iPad: Settings → Accessibility → Spoken Content → Voices → choose your language → download. Then use Safari.
Android: Settings → Accessibility → Text-to-speech output → Google Text-to-speech → Install voice data → your language. Then use Chrome.
Windows: Settings → Time & Language → Language & region → add your language → Language options → download Speech. Microsoft Edge also includes online voices.
Mac: System Settings → Accessibility → Spoken Content → System Voice → Manage Voices → your language → download.
If your language still isn't listed after installing, your device may not offer it — captions will still show.