multilingual multi-domain

hi, i have a multilingual multidomain drupal site and for some reason, he doesn't get the right language in the second domain.

I explain it in details :

- i have www.bruxelles-renouvelable.be who is in french and homepage is /node/1
-the other site is in dutch : www.hernieuwbaar-brussel.be and homepage is /nl/node/14

french is not the problem.... dutch is.
I try to create a php code that whe he sees that the adress begins with www.hernieuwbaar-brussel.be, he changes the language in dutch...
But it doesn't wok...
anybody could help me ?

function _i18n_get_lang() {

  switch($_SERVER['SERVER_NAME']) {
 
    case 'http://www.bruxelles-renouvelable.be':
      return 'fr';

    case 'http://www.hernieuwbaar-brussel.be':
      return 'nl';

  }