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="419" ns="0" title="Impeta z’ubutwari mu Rwanda rwo Hambere" />
      <page pageid="444" ns="0" title="Umurenge wa Gitega" />
      <page pageid="543" ns="0" title="Igiti cyitwa ‘Imana’" />
      <page pageid="581" ns="0" title="Itature ry ‘ingoma" />
      <page pageid="590" ns="0" title="Imyitirire ku mazina y&#039;inka" />
    </pages>
  </query>
</api>