Translation is always provided by DeepL. For some languages, transcription and translated speech are provided by external service partners. All source languages can be translated into any target language.
✓ provided by DeepL / ⎋ provided by an external service partner / — not available Transcription provided by external service partners (marked with ⎋) cannot yet auto-detect the source language,
which you must therefore specify explicitly.
GET /v3/languages?resource=voice and check for the transcription and translated_speech feature keys. The external flag on these features indicates if they are provided by an external service partner.
For audio format support and session limits, see Voice API Requirements. 
