Change fields names in the shipping form.

Hello there,

I am using WooCommerce + X Theme from Themeco, my WordPress installation is set up in fench.

I am trying to change some fields name in woocommerce/templates/checkout/form-shipping.php.
For instance, I change line 54 :
<h3><?php _e( 'Additional Information', 'woocommerce' ); ?></h3>
into
<h3><?php _e( 'Notes additionnelles', 'woocommerce' ); ?></h3>

but the form keep being displayed without my changes.

Any ideas ?

Cheers,
Julien