SOURCE

(function() {
  'use strict';
  // Your code here...
  var words = ['this','demo','man','so','cool'];
  var words2 = ['这','演示','男人','如此','帅气'];
	function underline(){
    for(var i=0;i<words.length;i++){
      document.body.innerHTML=document.body.innerHTML.replace(new RegExp(words[i],'ig'),'<a class="wavy">' + words2[i] + '</a>');
   	};
	};
  window.onload = underline;
})();

<h1>
  this is a demo
</h1>
<p>
  oh, this man is so cool!
</p>
<span>
  haa,it's sooo~ cooool~,
  <a id="go">
    I like this man
  </a>
</span>

body {
  color: #fff;
}

p {
  color: #a4a4a4;
}

a {
  color: #bfb;
}

a:hover {
  color: #ada;
  cursor: pointer;
}

.wavy {
  text-decoration:underline;
  text-decoration-style: wavy;
}

#go {
  width: 100px;
  height: 30px;
}