This tab is in the Settings dialog box. You use it to change or set languages. Later, you use the toolbar to select from these languages if the book will have more than one language.
Choose one or more languages.
Local Language
This is the language of the intended readers of monolingual books. It is the primary language in multilingual books.
Language 2 (e.g. National Language)
This language can be used in different ways. It is used in the front and back matter. Or, it can be used as a content language on inside pages, such as in a bilingual book.
If you want front and back matter to be in the same language as the book inside pages, choose the same language to match the Local Language.
Language 3 (e.g. Regional Language) (Optional)
If Local Language and Language 2 are the same, you need to choose a Language 3 if you want a bilingual book.
Sign Language (Optional)
You must choose a sign language here before you can publish your sign language book to the web.