Creates a preferred_admin_langcode column.
function user_update_8005() {
$spec = array(
'description' => 'The {language}.langcode that the user prefers for viewing administration pages.',
'type' => 'varchar',
'length' => 12,
'not null' => TRUE,
'default' => '',
);
db_add_field('users', 'preferred_admin_langcode', $spec);
}