This is from the episode "The Talons of Weng Chiang", which is truly hilarious. They don't really try to speak Chinese, unlike the dear folk of Firefly (epic Chinese fail, there), but it's still mock-worthy. And so...
[Edit: And now with English translations!]
This episode has Chinese in! Not good.
But mah Chinese r crap!
Okay, sit down and think. What am I going to do?!?
Heyy, if I pretended I could speak Chinese, would anyone know the difference?
Wait a sec. This is Victorian England! Nobody speaks Chinese!
Man, how am I such a mad genius?
I am so very cool.
BLAH BLAH BLAH CHATTER BLAH BLAH BLAH ETC
His accent sucks. DO NOT WANT.
Dr: Whut?
Magnus: D00d, your accent sucks.
DO NOT WANT