XML : Translating XML templates in Django

I am using Django 1.9 and have a XML template in the application's template folder, like this:

  {% load i18n %}  <!DOCTYPE document SYSTEM "http://www.reportlab.com/docs/rml.dtd">  <document filename="testdocument.pdf" colorSpace="CMYK" author="Me" title="Report">  ...    

I am placing {% trans "Foo" %} markers as usual, but makemessages -l <lang> doesn't create them in the .po file. HTML templates work fine.

How can I translate XML templates?