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Voice and language

Let callers speak in the language they are most comfortable using.

Configure up to four languages per agent from English, Spanish, French, German, Portuguese, Italian, Dutch, Hindi, Japanese, and Russian. Kai follows the caller's language and switches without a phone menu.

Kai listening carefully to a caller

Two to four

Languages per agent

Choose a unique set from the ten currently supported languages.

Automatic

Language following

Kai can follow the caller and switch among the languages you enabled.

Protected

Automatic restore

If a check fails, Kai restores the last verified agent setup.

Prerequisites

Start from a clean, working agent.

Multilingual setup updates an existing Vapi assistant. Make sure the current version is ready to become the rollback point before you change it.

Account and agent

Sign in as a business admin and open an agent that already has a Vapi assistant. Its inbound and outbound prompts must be available.

Clean starting point

Save or discard any unrelated draft first. KaiCalls takes a snapshot of the current assistant so it can restore that exact configuration if the checks fail.

Supported set

Choose two, three, or four unique languages.

Language selection is configured per agent. Enabling it on one agent does not change every agent in the business.

English
Spanish
French
German
Portuguese
Italian
Dutch
Hindi
Japanese
Russian

Dashboard setup

Select the languages, review the change, then run the checks.

  1. 1

    Open the caller-language settings

    Go to Dashboard → Agents → Edit → 4. Voice, then find Caller languages.
  2. 2

    Choose the supported languages

    Select between two and four unique languages from the supported set above.
  3. 3

    Review the planned update

    Confirm that the language set is correct and that the agent has no unrelated unsaved draft changes.
  4. 4

    Run checks and enable

    KaiCalls updates the language-related prompt and transcriber configuration, then evaluates the updated assistant before keeping it enabled.
The selected voice and unrelated assistant settings are preserved. The update changes the language instructions and the transcriber configuration needed for multilingual handling.

Evaluation gate

The built-in checks use text. They are not audio test calls.

KaiCalls runs sequential mock-conversation checks for the selected languages and switching behavior. The result determines whether the update stays in place.

Enabled

The update passed the evaluation gate and the multilingual configuration remains on the assistant.

Original settings restored

A check failed after the update. KaiCalls restored the assistant snapshot taken before setup began.

No changes applied

Setup stopped before the assistant was changed, so there is nothing to roll back.

Attention required

KaiCalls could not confirm a safe final state. Do not send customer traffic until the assistant configuration is reviewed and tested.

Real-world proof

A passing text check is only the first gate. Place real calls next.

Audio behavior, accents, names, addresses, and industry terms need to be heard and reviewed in the same conditions your callers will use.

  • Place an inbound test call in every selected language.
  • During at least one call, switch naturally between two configured languages.
  • Review the recording and transcript for the correct language, names, addresses, and business terms.
  • Confirm the agent still follows its qualification, booking, transfer, and fallback instructions.
  • Only direct customer traffic to the updated agent after those real-call checks pass.
KaiCalls preserves the voice you selected, but the built-in text evaluation does not prove that its accent or naturalness is right for every language. Listen to real audio before treating a language as production-ready.

Troubleshooting

When the update does not enable

The language picker will not continue

Confirm that you selected at least two and no more than four unique supported languages.

Original settings were restored

Review the agent instructions for single-language rules, correct them, and run the update again.

The result says attention is required

Stop customer traffic to that assistant and review its current Vapi configuration before retrying.

Text passes but the call sounds wrong

Use the recording and transcript to identify pronunciation, voice, or terminology issues. The text check does not validate audio quality.

For developers

The same protected update is available through the public API.

Send POST /api/v1/agents/enable-multilingual with an API key that has the agents:write scope. The public API body uses agent_id; dashboard code uses agentId.

See the API reference for authentication and request details.

    How to Enable Multilingual Calling | KaiCalls Help