By default, symfony puts lang="en"
on every single page of your project.
If your application deals with other languages than english, go to your apps/frontend/templates/layout.php
file and change the second line:
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="<?php echo $sf_user->getCulture() ?>"↵
lang="<?php echo $sf_user->getCulture() ?>">