Fix list item classes.

includes/navigation.inc > hook_links()
The $class array is not initiated at the start of the iteration and this causes an increment of the menu items classes.

ex :

<li class="nav__item nav__item--en-US active">...</li>
<li class="nav__item nav__item--en-US active nav__item nav__item--fr">...</li>
...

To fix that all you have to do is to replace line 110 in includes/navigation.inc :

foreach ($links as $key => $link) {
      // Add default core classes if wanted.
      if (!$only_use_smacss) {
        $class = array($key);
      }

By

foreach ($links as $key => $link) {
      $class= array();
      // Add default core classes if wanted.
      if (!$only_use_smacss) {
        $class = array($key);
      }