Nhentai().book_language() - exentio/nhentai_api GitHub Wiki

Nhentai().book_language(book_id, return_string = False)

Gets the language of a book, the result is alphabetically sorted (often there's the tag "translated").

Returns a list if the ID is the only parameter; instead if return_string is set to True, it returns a str.
If there is no info about the language, the only content of the list is no language info.