Daughter of Tepes
I've actually never seen someone spell it "Lävatein". I've always seen it spelled the proper way. Even Castlevania spells it the right way.
How nice. It's been the opposite for me. I've seen it spelled with a single N and/or with "ä" or "a" most of the time. Either that or, only once or twice, approximations like "Levantine" or "Leviathan".
Daughter of Tepes
The more correct translation for Hisoutensoku would be "Lacking Perception of the Natural Laws of the East" or "Lacking Perception of the Rule of Heaven in the East". Of course that's much to tedious to say, so I just say 'Soku personally.
Hm, I prefer to say Hisoutensoku because I think it sounds pretty.