@Felthry I went down that rabbit hole a few years ago. The rules seem arbitrary, but there is a purpose to them. The whole point is to be quickly and easily identified at a distance, so folks could tell which guy in identical armour was which on the battlefield. The rules are meant to increase contrast and visibility between design elements to aid with this.
The reason it's all in Old French is that's what the English nobility all spoke when this was established as common practice.
@Felthry They're supposed to look fierce. In heraldry, the griffin is a bold statement of power, as it combines the lion, the "king of beasts", with the eagle, the "king of birds".
Yes, I know, that's just how they thought back then.