Revealing mistake: When Rick catches himself in the neck with the fish-hook, if you look closely when Rick pulls on it, it's pretty obvious that it's a prosthetic. Not only is the skin around the hook a lighter shade than the rest of his neck, but the way it stretches and wrinkles is completely unrealistic, giving it away as a small sheet of latex.
Continuity mistake: When Yuan fights the Emperor, shortly after the Emperor realises she's mortal, she leaps towards him and twirls through the air. If you look close, her sword swaps hands between cuts when it connects with the Emperor's sword. First it's in her right hand, then her left hand, then it's back in her right hand. It looks like the left-hand shot was an alternate take of the shot right after, and they flipped it horizontally to create a "different camera angle" in editing, hence the hand-swap.
Continuity mistake: When Wilson meets Rick and Evie at the museum, pay attention when Rick delivers the line about giving them a heads up next time Wilson takes Alex on one of "his fieldtrips." In the first shot, Wilson's arms at down at his side. In the next shot, suddenly they are up and he's patting his chest while saying "Yes, of course." The shots are back-to-back, so there's no time for him to have lifted his arms between edits.
Continuity mistake: When Mad Dog is flying the O'Connell's and Lin in the plane, Mad Dog remarks that he can't guarantee they'll live, and it cuts to a close-up of Rick sarcastically saying "Great!" Watch Alex... he goes from facing his left to facing his right between edits.
Continuity mistake: When Lin is explaining what needs to happen at the club, pay attention when she says the lines "Once the diamond is placed at the top, it will point the way to Shangri-La. Yang still has the diamond..." There are a series of cuts throughout these lines, and Lin goes from facing forward towards Alex to facing sideways towards Rick between two of the edits.
Other mistake: In the final scene, watch the drummer in the band. He's not making any contact with the drums and is just miming it. Ex. He stops his drumstick about 2" above the cymbal every time he's supposed to hit it, even though you can hear a cymbal in the soundtrack. It's most noticeable when the brand briefly goes into focus as the camera passes between Alex/Lin and Rick/Evie. (He was probably told not to actually drum so the dialogue wouldn't be ruined).
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.