I've been playing some Fire Emblem recently and I noticed that the English translation for ドラゴンナイト is Wyvern Rider. My initial guess that there wasn't a word for Wyvern in Japanese was wrong though as ワイバーン exists. So I was wondering what the nuance and difference between the two in Japanese is along with what differences there are with 竜.
龍 or the simplified 竜 both represent dragons, but not necessarily occidental ones. Since there are differences between Eastern and Western ideas of dragons (some relatively minor, some major) it is good to keep these separate.
ドラゴン would be a medieval European image of a dragon (LOTR, GoT). A wyvern is considered smaller, with two legs instead of four, without the intelligence or special properties normally reserved for dragons. A beastly lesser cousin of the dragon.
In Japan, the distinction between dragon and wyvern is likely unclear for most people, and the word wyvern is much lesser known. Likely for this reason the original naming chose 'dragon'. As wyvern is relatively better known among English speakers, however, the translation reflected this.