Hello @Chuong Phung , Thanks for using Microsoft Q&A Platform.
The pre-built models in Form Recognizer support several languages. When using a pre-built model API, the language is automatically detected and extracted from the document. It is not necessary to define the locale as it is an optional parameter.
If you intend to use a custom model, it is same. However, you can still set the locale (optional) request parameters to the appropriate language code, such as "en-US" for English (United States). This will ensure that the custom model is trained on documents in the language specified. I don't think adding locale in the document helps.
Please refer to this documentation to add locale code and to request URL: https://westus.dev.cognitive.microsoft.com/docs/services/form-recognizer-api-2022-08-31/operations/AnalyzeDocument
We are unsure of the API version you were using, whereas we are referring to the API version 2022-08-31.
Is this something you are looking for?
I hope this helps.
Regards,
Vasavi
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