Revealing mistake: During a large battle scene between the Fire Nation and the Northern Water Tribe, the camera pans to reveal a Fire Nation soldier fighting with no one.
Revealing mistake: During the first conversation between Fire Lord Ozai and General Zhao we can see that Ozai's eyes move from left to right while he looks in the direction of Zhao's chest, this revealing the use of a prompter.
Answer: The TV show Americanized the pronunciations whereas the movie said them correctly.
The show is American, so with original characters you're allowed to say them how you want.