I was just going to mention that, but you beat me to it. It's just bizarre to use XML external entities for internationalization.

I worked on TomTom Home, which was implemented in xulrunner, and I developed some internationalization/localization tools that had to deal with XUL DTDs as well as several other different and incompatible file formats for storing translations. I could never for the life of me figure out why they decided to use DTDs with external entities for translations.