Its not a phrase, yes; but its not hardcoded either. This text can be changed by an Administrator via:
Admin Panel » Options » Spam Management » Spam Cleaner Email Text
Moving it to a properly phrased Email Template would be ideal!
It is in the options to make it easier to change than a phrase in the average case, though yes I can see an issue with it not being changed with a language pack. That said, moving it to a phrase creates multi-language install issues.
