Multilingual Voice Agents

Pick the right STT and TTS models for a voice agent that speaks more than one language.

A multilingual voice agent has two model decisions: which STT model transcribes the user, and which TTS model speaks the agent. Pick each one based on what your agent needs to do at runtime.

Pick your STT model

Your situation	Use this
Conversational agent in one of the 10 Flux Multilingual languages, with turn awareness and barge-in	Flux Multilingual (`flux-general-multi`)
Single known language, all calls	Flux Multilingual with a single-entry `language_hints` array, or the language-specific Nova model
Multilingual support center, calls arrive in different languages	Flux Multilingual with multiple entries in the `language_hints` array
Code-switching mid-conversation, no need for turn awareness	Nova-3 with `language: "multi"`

Flux Multilingual is the default recommendation. It handles turn awareness and interruption with the same low latency as flux-general-en. Use Nova-3 only when you need code-switching but not the conversational features.

Flux Multilingual configuration

agent.listen.provider.type: deepgram
agent.listen.provider.version: v2
agent.listen.provider.model: flux-general-multi
agent.listen.provider.language_hints: array of one or more BCP-47 codes (optional)

1 {
2   "agent": {
3     "listen": {
4       "provider": {
5         "type": "deepgram",
6         "version": "v2",
7         "model": "flux-general-multi",
8         "language_hints": ["en", "es"]
9       }
10     }
11   }
12 }

The language_hints parameter biases the model toward specific languages and improves accuracy. With no hints, the model auto-detects the spoken language. Pass one hint for known-language calls and multiple hints for multilingual support centers. See Flux Multilingual & Language Prompting for the full hint reference and supported languages.

When you use flux-general-multi, user ConversationText events include languages_hinted and languages fields. See Conversation Text.

Nova-3 multi configuration

agent.listen.provider.model: nova-3
agent.listen.provider.language: multi

Pick your TTS model

Your situation	Use this
Bilingual English/Spanish agent	Deepgram Aura codeswitching voice
Any other multilingual mix	Cartesia, OpenAI, or Eleven Labs with `language: "multi"`

Deepgram Aura codeswitching (English/Spanish)

Aura ships five voices that switch between English and Spanish naturally inside one response: Aquila, Carina, Diana, Javier, and Selena.

agent.speak.provider.type: deepgram
agent.speak.provider.model: aura-2-aquila-es (or aura-2-carina-es, aura-2-diana-es, aura-2-javier-es, aura-2-selena-es)

These voices handle mixed-language responses without switching providers. See TTS Models for the full Spanish voice catalog.

Third-party multilingual TTS

For other language combinations, set the speak provider to OpenAI, Eleven Labs, or Cartesia and pass agent.speak.provider.language: "multi". For Eleven Labs, this parameter maps to language_code.

Prompt for the language behavior you want

LLM behavior varies by provider. The prompt steers the agent toward a specific language strategy.

Goal	Prompt pattern
Mirror the user’s language turn by turn (English ↔ Spanish ↔ English)	“Match the language of each user message independently.”
Force the agent to speak one language regardless of user input	”Always respond in English, even if the user speaks another language.”
Default to one language but mix in another when relevant	”Respond in English unless the user speaks Spanish; if Spanish, mix Spanish and English naturally.”

1	{
2	"agent": {
3	"listen": {
4	"provider": {
5	"type": "deepgram",
6	"version": "v2",
7	"model": "flux-general-multi",
8	"language_hints": ["en", "es"]
9	}
10	}
11	}
12	}