Curiously enough, the game had German subtitles anyway (although they were for other German speaking countries like Austria). That was pretty convenient for German fans of the game, that could import it relatively easily.
Disowned Adaptation: Itagaki did not like Ninja Gaiden Sigma, going as far as to refuse to sign copies of it. This probably has something to do with the fact that he wasn't involved with this particular version of the game (since, objectively, it's not very different from Black). However, he did admit that it gave PS3 owners a shot at the game. And all of the new features in Sigma were carried over to Ninja Gaiden II at the end.
The Other Darrin: English localization just can't get a hold of a voice actor for too long. As of Ninja Gaiden III, there are three different actors for each main release. Troy Baker reprises his role, having provided his voice in Dead of Alive Dimensions. Compare and contrast to Hideyuki Hori, who has been voicing Ryu for 16 years, the first of which was the originalDead or Alive back in 1996.
Word of God: According to this interview, the folks at Tecmo were quite unsure on how to translate the video game's title ("Ninja Ryūkenden", which means "Ninja Dragon Sword Legend") for the foreign players, so they opted for Rule of Cool even if it didn't make much sense.