In all seriousness, Koji Fox actually talked about this before, (paraphrasing) he explained his choice of language by comparing plain English to eating normal meals every day and the dialog in this game to having a dessert every now and then.

What Koji Fox overlooked there is that instead of having regular meals every day, now we're having desserts every day for 4 years + however long this game will last, having dessert in place of every meal is as bad if not worse than plain meals, and I really hope the people in Ilsabard or the New World at least use plain English so we can get a break of the same old dialog.