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">Mediji</ns>
      <ns id="-1" case="first-letter" canonical="Special" xml:space="preserve">Posebno</ns>
      <ns id="0" case="first-letter" content="" xml:space="preserve" />
      <ns id="1" case="first-letter" subpages="" canonical="Talk" xml:space="preserve">Razgovor</ns>
      <ns id="2" case="first-letter" subpages="" canonical="User" xml:space="preserve">Suradnik</ns>
      <ns id="3" case="first-letter" subpages="" canonical="User talk" xml:space="preserve">Razgovor sa suradnikom</ns>
      <ns id="4" case="first-letter" canonical="Project" xml:space="preserve">Horvatian Wiki</ns>
      <ns id="5" case="first-letter" subpages="" canonical="Project talk" xml:space="preserve">Razgovor Horvatian Wiki</ns>
      <ns id="6" case="first-letter" canonical="File" xml:space="preserve">Datoteka</ns>
      <ns id="7" case="first-letter" subpages="" canonical="File talk" xml:space="preserve">Razgovor o datoteci</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">MediaWiki razgovor</ns>
      <ns id="10" case="first-letter" canonical="Template" xml:space="preserve">Predložak</ns>
      <ns id="11" case="first-letter" subpages="" canonical="Template talk" xml:space="preserve">Razgovor o predlošku</ns>
      <ns id="12" case="first-letter" canonical="Help" xml:space="preserve">Pomoć</ns>
      <ns id="13" case="first-letter" subpages="" canonical="Help talk" xml:space="preserve">Razgovor o pomoći</ns>
      <ns id="14" case="first-letter" canonical="Category" xml:space="preserve">Kategorija</ns>
      <ns id="15" case="first-letter" subpages="" canonical="Category talk" xml:space="preserve">Razgovor o kategoriji</ns>
    </namespaces>
  </query>
</api>