Migrating XML source twice, according to language
Turns out I didn't look at SimpleXML enough.

Using XPath, I can very easily select one of the languages through the lang attribute, and as such have one language imported.

If i then make a second migration for the other language, my problem is solved.

For reference, the selector for the description now looks like this:

$this-&gt;addFieldMapping('body', 'desc')
  -&gt;xpath('desc[@lang="nl"]');