If the contents of the book translated into another language, then disappears into the book of navigation.
Navigation in the original language is, the translation was not.

function book_node_load($nodes, $types) {
  $result = db_query("SELECT * FROM {book} b INNER JOIN {menu_links} ml ON b.mlid = ml.mlid WHERE b.nid IN (:nids)", array(':nids' =>  array_keys($nodes)), array('fetch' => PDO::FETCH_ASSOC));
  foreach ($result as $record) {
    $nodes[$record['nid']]->book = $record;
    $nodes[$record['nid']]->book['href'] = $record['link_path'];
    $nodes[$record['nid']]->book['title'] = $record['link_title'];
    $nodes[$record['nid']]->book['options'] = unserialize($record['options']);
  }
}

translation is not considered material

Comments

orb’s picture

orb CreditAttribution: orb commented 
if ($view_mode == 'full' && $node->nid != $node->tnid && $node->tnid != 0) {
    $tnode = array($node->tnid => (object)$node->tnid);
    book_node_load(&$tnode, array($node->type => $node->type, ));
    $node->scalar = $tnode[$node->tnid]->scalar;
    $node->book = $tnode[$node->tnid]->book;
    $node->content['book_navigation'] = array(
      '#markup' => theme('book_navigation', array('book_link' => $node->book)),
      '#weight' => 100,
    );
  }

Version: 7.10 » 7.x-dev

Core issues are now filed against the dev versions where changes will be made. Document the specific release you are using in your issue comment. More information about choosing a version.