Audio problem: When Jonathan leaves at the very end of the film, watch the valet's face. When he says the lines "Let me get your bags, sir" and "Where you off to, Mr. Carnahan?", it's very clear he's not actually saying the lines. In fact, his chin/mouth are barely moving at all. Jonathan's dialogue "Don't touch it, don't touch it!" also seems to not match. It seems like every single line in the scene before "Step on it, I've got a plane to catch!" was either (poorly) dubbed or added during post-production.
Audio problem: When the Yeti kicks a "goal" with the soldier and the gate, pay attention to the shots and the soldier's scream. In the second shot, the soldier is an instant away from hitting the gate - he's literally only a few feet away from it. Then it cuts to a shot of the Yeti watching, and you hear the soldier continuing to yell for several seconds, even though you should hear him hit the gate. It then cuts back to the soldier and he finally hits the gate. The timing of the scream makes no sense.
Audio problem: When the O'Connells and Lin meet at the club and Lin is explaining what needs to happen next, at one point she says the line "beyond it is a golden tower." If you look closely, the words she's saying and her mouth movements don't quite match. (Only the word "tower" matches... nothing else.) It's an over-the-shoulder shot of her, and her mouth is a little out-of-focus, but you can tell. The line was very likely redubbed in post-production, and thus wasn't said at exactly the same speed.
Audio problem: When Yang is about to bring the Emperor to life, he says "Once this touches him, the Emperor will rise... to rule again!" When he says "to rule again!" his mouth is closed. It's a very wide shot, so you have to look closely to notice... but his mouth is definitely closed.
Audio problem: When the Emperor is about to show Juan the execution of General Ming, there's a wide shot, and he says the line "Come, I want to show you something." If you look closely though, his mouth is closed the entire line.
Audio problem: During the final scene, when Mad Dog says "Evening girls! You're looking well!" and "Ooo! It's a fine night to be me!" his mouth isn't moving. They almost get away with it because his face is partially obscured for the first line, but you can still see that he isn't actually speaking.
Answer: Reading and speaking many Eastern languages can be entirely different tasks so it's perfectly plausible that she knew how to translate the writing but not how to speak it.