php 和 js互相调用

<script src="/assets/js/lang/cn.js"></script>
<script src="/assets/js/lang/vietnam.js"></script>
<script type=text/javascript>
   var currentLang = localStorage.getItem('currentLang');
    var useLang = {}
    if(currentLang) {
      switch(currentLang) {
         case 'cn':
          useLang = cn;
         break;
         case 'vietnam':
          useLang = vietnam;
         break;
       }
    } else {
      localStorage.setItem('currentLang', 'cn');
      useLang = cn;
    }
</script>
    <? $key="<script type=text/javascript>document.write(useLang['bet'])</script>"; echo $key;?>