In which cases should I specify the source language?
DeepL can automatically recognize the language of a text. The reliability of the result increases with the length of the text, and short texts can sometimes lead to incorrect results.
If you specify the language of the text in a query, DeepL Translator always uses that language. If you know the language of the source text, you should use the source_lang parameter to specify the corresponding code.
Please consult the API documentation for a complete list of all supported source languages.