I just assumed the "s" got lost in the translation, it is from French to English I think. I suppose you could call it the Plague Lord - meaning Cadak - but it sounds harder for LW to fight against the Plague Lords as it implies more foes than the singular. After all the Kai Grand Master has just destoyed the Darklords he needs an even greater challenge.
We'll have to wait and see what the cover looks like with the wording when it is advertised as an upcoming release, although now it has been mentioned I'm sure the mistake will be rectified - if in fact it was a mistake in the first place.
Well spotted though, I didn't notice. :wink: