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>
    <namespaces>
      <ns id="-2" case="first-letter" canonical="Media" xml:space="preserve">Media</ns>
      <ns id="-1" case="first-letter" canonical="Special" xml:space="preserve">Istimewa</ns>
      <ns id="0" case="first-letter" content="" xml:space="preserve" />
      <ns id="1" case="first-letter" subpages="" canonical="Talk" xml:space="preserve">Pembicaraan</ns>
      <ns id="2" case="first-letter" subpages="" canonical="User" xml:space="preserve">Pengguna</ns>
      <ns id="3" case="first-letter" subpages="" canonical="User talk" xml:space="preserve">Pembicaraan Pengguna</ns>
      <ns id="4" case="first-letter" subpages="" canonical="Project" xml:space="preserve">RPGFWIDWiki</ns>
      <ns id="5" case="first-letter" subpages="" canonical="Project talk" xml:space="preserve">Pembicaraan RPGFWIDWiki</ns>
      <ns id="6" case="first-letter" canonical="File" xml:space="preserve">Berkas</ns>
      <ns id="7" case="first-letter" subpages="" canonical="File talk" xml:space="preserve">Pembicaraan Berkas</ns>
      <ns id="8" case="first-letter" subpages="" canonical="MediaWiki" xml:space="preserve">MediaWiki</ns>
      <ns id="9" case="first-letter" subpages="" canonical="MediaWiki talk" xml:space="preserve">Pembicaraan MediaWiki</ns>
      <ns id="10" case="first-letter" canonical="Template" xml:space="preserve">Templat</ns>
      <ns id="11" case="first-letter" subpages="" canonical="Template talk" xml:space="preserve">Pembicaraan Templat</ns>
      <ns id="12" case="first-letter" subpages="" canonical="Help" xml:space="preserve">Bantuan</ns>
      <ns id="13" case="first-letter" subpages="" canonical="Help talk" xml:space="preserve">Pembicaraan Bantuan</ns>
      <ns id="14" case="first-letter" canonical="Category" xml:space="preserve">Kategori</ns>
      <ns id="15" case="first-letter" subpages="" canonical="Category talk" xml:space="preserve">Pembicaraan Kategori</ns>
    </namespaces>
  </query>
</api>