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AssemblyAI supports a wide range of languages across our speech-to-text models for pre-recorded audio. The available languages vary by model. Check out the Models page to learn more about our different models and how to choose the best one for your use case. See our Model selection page for more details on specifying a model in your request.

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Universal-3.5 Pro

Universal-3.5 Pro supports the following 18 languages. To automatically fall back to Universal-2 for anything outside this set, set speech_models to ["universal-3-5-pro", "universal-2"] and set language_detection to true.

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Regional dialects and variants

Universal-3.5 Pro goes beyond standard language support with deep understanding of regional dialects and local variants. Whether your audio features Quebecois French, Mexican Spanish, or Brazilian Portuguese, the model accurately captures speech as it’s naturally spoken — including colloquial expressions, local vocabulary, and accent-specific pronunciation patterns.
Dialect supportYou do not need to specify a dialect code to get accurate dialect transcription. Universal-3.5 Pro automatically recognizes regional speech patterns when using the base language code (e.g., fr for all French dialects, es for all Spanish dialects).

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Universal-2

Universal-2 supports 99 languages. Pass the corresponding language_code in your transcription request to specify the language.

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Accuracy metrics

The following groups Universal-2 languages by transcription accuracy, measured by Word Error Rate (WER).
English, Spanish, French, German, Indonesian, Italian, Japanese, Dutch, Polish, Portuguese, Russian, Swedish, Turkish, Ukrainian, Catalan
Arabic, Azerbaijani, Bulgarian, Bosnian, Mandarin Chinese, Czech, Danish, Greek, Estonian, Finnish, Galician, Hebrew, Hindi, Croatian, Hungarian, Korean, Macedonian, Malay, Norwegian, Romanian, Slovak, Swiss German, Tagalog, Thai, Urdu, Vietnamese
Afrikaans, Belarusian, Welsh, Persian (Farsi), Armenian, Icelandic, Kazakh, Lithuanian, Latvian, Maori, Marathi, Slovenian, Swahili, Tamil
Amharic, Assamese, Bengali, Gujarati, Hausa, Javanese, Georgian, Khmer, Kannada, Luxembourgish, Lingala, Lao, Malayalam, Mongolian, Maltese, Burmese, Nepali, Occitan, Punjabi, Pashto, Sindhi, Shona, Somali, Serbian, Telugu, Tajik, Uzbek, Yoruba

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Unsupported feature behavior

Not all features are available for every language. If you enable a feature that isn’t supported for the language of your audio, the API’s behavior depends on how the language was specified:
  • With language_code (manual): The API rejects the request and returns an error, such as "The following models are not available in this language: speaker_labels". This lets you catch configuration issues before processing.
  • With language_detection (automatic): The request completes normally, but any features that aren’t supported for the detected language are silently omitted from the response. The transcription itself still succeeds. This is because the language isn’t known until after the request is submitted, so the API can’t validate feature compatibility upfront.
To avoid unexpected results when using Automatic Language Detection, use the language_code and language_confidence fields in the response to verify the detected language and handle cases where a feature may not have been applied.