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Legacy Multilingual setting is deprecated

The legacy scalar value "multi" of the agent language field is deprecated in favor of the explicit locale-array form (e.g. ["en-US","es-ES"]). The array form is supported on the same language field and lets you pick the exact set of languages your agent should handle, which improves accuracy compared to the static 10-language "multi" set. Affected APIs: What’s changing on 07/31/2026:
  1. The scalar "multi" value of language will be rejected by the Create Agent, Update Agent, Create Chat Agent, and Update Chat Agent endpoints.
  2. The dashboard’s legacy Multilingual toggle will be removed.
  3. Existing agents that still have language: "multi" will be automatically migrated by Retell to the equivalent locale array (["en-US", "es-ES", "fr-FR", "de-DE", "hi-IN", "ru-RU", "pt-PT", "ja-JP", "it-IT", "nl-NL"]). No action is required on your existing agents.
Action required for API integrators: If your client code constructs agent payloads with "language": "multi", update it to send the locale array form before 07/31/2026. After that date, requests using the scalar "multi" value will be rejected. For better accuracy, narrow the array down to the languages your agent actually needs — see the accuracy trade-offs in Configure a multilingual agent. 
{
  "language": "multi"
}
Also update any code that reads agent configurations and branches on language === "multi", since after the automatic migration the field will return the array form instead. Effective date: After 07/31/2026, agents created or updated with language: "multi" will be rejected. Existing agents are migrated automatically on or before this date.