You are looking at the HTML representation of the XML format.
HTML is good for debugging, but is unsuitable for application use.
Specify the format parameter to change the output format.
To see the non HTML representation of the XML format, set format=xml.
See the complete documentation, or API help for more information. 
<?xml version="1.0"?>
<api>
  <query>
    <pages>
      <page pageid="500" ns="0" title="FAQ Weewx" />
      <page pageid="504" ns="0" title="Weather Display para Raspberry Pi" />
      <page pageid="513" ns="0" title="¿Donde puedo localizar los driver del datalogger para Windows XP?" />
      <page pageid="547" ns="0" title="FAQ WX" />
      <page pageid="565" ns="0" title="VUE" />
      <page pageid="583" ns="0" title="Visual Star Meteoclimatic" />
      <page pageid="621" ns="0" title="Sotware webcam" />
    </pages>
  </query>
</api>