Set defaultLanguage to source site's language by default

I ran into an issue migrating body text, where it's content disappeared in the edit form.
http://drupal.org/node/1823512

The gist of it is that the defaultLanguage is "und", when I change it to "nl" (my default) my problems where solved. Maybe defaultLanguage should be filled with the default language of a website, gathered automatically from the website settings?