Here's a link to my xliffRoundTrip Tool that I offer as open source software at sourceforge.
I wrote it at the request of the OASIS XLIFF TC (of which I am the chair)
This published version is best for document-centric, single XML files.
I've written, and demonstrated a DITA-specific version of the tool that reads the DITA Map, and generates XLIFF out of the many topics in the map (also works on SVG files). http://xmarker.com/xliffutilities/
There is a Drupal module, XLIFF Tools, that uses my xliffRoundTrip engine. The makers have asked me to make a specific engine specifically for this module (which I've done)