Youkai Watch has been Trademarked as Yo-Kai Watch in the U.S., LOL but true.

[jigokutamago]

Nothing strange about the spelling change. The Japanese pronunciation of Youkai or Yōkai is closer to Yo-Kai than you kai. An example http://www.forvo.com/word/youkai/

 

You would also think that they would translate the word Youkai, but it is hard to find a word that directly corresponds in English.