Perhaps there really isn't one.:sweat:
Let's go ask Jackie Chan! (was gonna say Takuya, but he already replied).
& besides, at the end of the cartoon series, they used to have that "Ask Jackie" thing. If anyone can contact him here, I believe you can Keith. :anime:
Maybe there isn't an exact equivalent in the language. More likely other synonyms would be used instead, like hobbyist, aficionado, or more specifically "one who is obsessed with [Insert subject/topic here]."
I just asked my mom about it. She had to think for a while, haha...but there's a term, "dai zi," which literally refers to someone who stays still. But it's used to refer to bookworms and people of that effect...so even if there's no specific word for "nerd" or "geek," there's definitely terms that fit the context. It's just how languages work.