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OverviewAPI ReferencePre-recorded STTStreaming STTVoice AgentsSpeech UnderstandingGuardrailsLLM GatewayFAQ
  • Getting started
    • Transcribe a pre-recorded audio file
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  • Models
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  • Features
    • Boost specific terms
    • Label speakers
    • Transcribe multiple audio channels
    • Transcribe audio with mixed languages
      • Detect language automatically
      • Set language manually
      • Supported languages & features
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    • Include filler words
    • Search for words in transcript
    • Set the start and end of the transcript
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  • Unsupported feature behavior
  • Universal-3 Pro
  • Regional dialects and variants
  • Universal-2
FeaturesLanguages

Supported Languages & Features

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AssemblyAI supports a wide range of languages across our speech-to-text models for pre-recorded audio. The available languages and features 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.

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, check the feature tables below to confirm which features are available for the languages you expect in your audio. You can also 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.

Universal-3 Pro

Regional dialects and variants

Universal-3 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 support

You do not need to specify a dialect code to get accurate dialect transcription. Universal-3 Pro automatically recognizes regional speech patterns when using the base language code (e.g., fr for all French dialects, es for all Spanish dialects).

English dialects and variants
Dialect / VariantDescription
American EnglishStandard US English, including regional variants (Southern, Midwestern, Northeastern)
British EnglishUK English, including Received Pronunciation and regional accents
Australian EnglishAustralian English with local expressions and pronunciation
Spanish dialects and variants
Dialect / VariantDescription
Castilian SpanishStandard Peninsular Spanish as spoken in central and northern Spain
Mexican SpanishMexican Spanish with local vocabulary and pronunciation
Argentine SpanishRioplatense Spanish with distinctive voseo and pronunciation
Colombian SpanishColombian Spanish with regional speech patterns
Chilean SpanishChilean Spanish with rapid speech patterns and local slang
Caribbean SpanishCuban, Dominican, and Puerto Rican Spanish dialects
SpanglishEnglish-Spanish code-mixing common in US bilingual communities
French dialects and variants
Dialect / VariantDescription
Metropolitan FrenchStandard Parisian French
Canadian French (Quebecois)Quebec French with distinctive vocabulary, pronunciation, and expressions
Belgian FrenchBelgian French with local vocabulary and pronunciation
Portuguese dialects and variants
Dialect / VariantDescription
Brazilian PortugueseBrazilian Portuguese with local vocabulary, pronunciation, and expressions
European PortugueseStandard Lisbon Portuguese with Iberian pronunciation
Italian dialects and variants
Dialect / VariantDescription
Standard ItalianStandard Italian based on Tuscan-influenced speech

Universal-2

Breakdown of Universal-2 language support

High accuracy (≤ 10% WER)

English, Spanish, French, German, Indonesian, Italian, Japanese, Dutch, Polish, Portuguese, Russian, Swedish, Turkish, Ukrainian, Catalan

Good accuracy (>10% to ≤25% WER)

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

Moderate accuracy (>25% to ≤50% WER)

Afrikaans, Belarusian, Welsh, Persian (Farsi), Armenian, Icelandic, Kazakh, Lithuanian, Latvian, Maori, Marathi, Slovenian, Swahili, Tamil

Fair accuracy (>50% WER)

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