1. Detect the incoming language: Speech to Text The input for this requirement is a live audio stream (a phone call). To process this, you must use the Speech to Text service, which specifically includes a Language Identification feature. This capability analyzes the audio input to determine the spoken language (e.g., distinguishing between French and English) before or during transcription. Services like Text Analytics or Translator require text input, making them unsuitable for the initial detection from raw audio.

2. Respond in the callers' own language: Text to Speech "Responding" in a call handling context implies generating an audible voice reply. The Text to Speech service is designed to convert the system's text-based responses into synthesized, human-like spoken audio in the specific target language identified (French or English).

Microsoft Learn. (n.d.). What is the Speech service? Retrieved from https://learn.microsoft.com/en-us/azure/ai-services/speech-service/overview

Relevance: Confirms that the Speech service provides "Language identification" to "identify languages spoken in audio" and "Text to speech" to "convert input text into human-like synthesized speech."

Microsoft Learn. (n.d.). Implement language identification. Retrieved from https://learn.microsoft.com/en-us/azure/ai-services/speech-service/language-identification

Relevance: Details how "Speech to text recognition" is used when you need to "identify the language in an audio source."

Microsoft Learn. (n.d.). Text to speech overview. Retrieved from https://learn.microsoft.com/en-us/azure/ai-services/speech-service/text-to-speech

Relevance: Validates that Text to speech enables applications to convert text into synthesized speech, supporting the requirement to "respond" vocally.