In language file for site. Line 87 is this:
COM_ABOOK_AUTHOR_THIS-BOOK="Authors of this book"
Should it be:
COM_ABOOK_AUTHOR_THIS_BOOK="Authors of this book"
The problem with this was that the string was not translated to swedish but was in english. But if I changed to: COM_ABOOK_AUTHOR_THIS_BOOK in the english and swedish language files and in components\com_abook\views\book\tmpl\default.php it was translated.