Rename node.language field to node.langcode.
function node_update_8002() {
$spec = array(
'description' => 'The {language}.langcode of this node.',
'type' => 'varchar',
'length' => 12,
'not null' => TRUE,
'default' => '',
);
db_change_field('node', 'language', 'langcode', $spec);
}