The Language Detection feature of the Azure Text Analytics REST API evaluates text input for each document and returns language identifiers with a score that indicates the strength of the analysis.
The Language Detection feature can detect a wide range of languages, variants, dialects, and some regional or cultural languages. The exact list of languages for this feature isn't published.
If you have content expressed in a less frequently used language, you can try the Language Detection feature to see if it returns a code. The response for languages that can't be detected is unknown.