<script>
if(navigator.browserLanguage) {  
      var language = navigator.browserLanguage;    
   }
   else if(navigator.language) {
      var language = navigator.language;
   }
   
   switch (language.substring(0,2))  {
      case "pt" : location.href="pagina_em_portugues.php";
         break;
      case "en" : location.href="pagina_em_ingles.php";
         break;
      case "es" : location.href="pagina_em_espanhol.php";
         break;
      default : location.href="pagina_em_portugues.php"; 
}
</script>