English equivalent of two popular Chinese slang terms: 学霸 (academic overlord) and 学婊 (academic bitch)

Translation is difficult, and translation of slang is even more difficult because of all the non-shared cultural context and nuances involved. So there's usually not a direct translation (one-to-one always) that fits for slang. Often that results in a direct loan word, like 'kow tow' or 'kung fu', or loan translation, like 'brain washing' or 'lose face'. This happens more often than a direct loan because the phonology and culture are so different between English and Chinese.

For these two terms, 学霸 ('school tyrant') and 学婊 ('school whore/bitch') (those are the character for character translations, the nuance of the individual words may or may not be very misleading), there are no such terms for the direct corresponding cultural situation, especially for the second one which seems to be a recent invention. Of course there are terms in the same area of concern (academic excellence):

• valedictorian (n, formal) - the best in the class
• overachiever - someone who looks like they're trying really hard (and is succeeding at everything)
• teacher's pet - slang, the student that the teacher seems to favor over all others (maybe academically or because they are controllable) not derogatory but usually used disparagingly or enviously.
• kiss-ass (n) slang, (not primarily academic) someone who does things just to please a superior (a teacher's pet might be a kiss-ass, but that is not at all necessary)
• nerd - academically oriented to the exclusion of all else (compare with dweeb and dork).
• swot (n) swotty (adj) - chiefly Br slang, very studious
• cutthroat (adj) for a person or atmosphere, a very competitive academic environment, where people will break the rules to get ahead

I'd prefer to have many more terms in that area of which there are many I am sure, I just can't think of them.

"学霸" (literally meaning "academic overlord") to refer to someone who does very well in his/her study and who always achieve high grades in exams.

I believe the equivalent is straight A student. It is used for students who always get high grades (to get straight A's).

Derogatory alternatives are grind (US slang) and swot (BR slang).

"学婊" (literally meaning "academic bitch") when we (jokingly, without any malicious meaning) speak of someone who does excellently in his/her study but who likes hiding it from the others

I don't believe there is a good equivalent for this in English. For example, someone might pretend not to study to seem like a natural genius.

It is also mentioned as a strategy of self-handicapping.

However, in a twitter message, this kind of person is directly called a bitch. As you know, bitch is usually an insult but it can be used in a positive sense informally for someone who is performing well (and probably used out of jealousy).

It's important to remember that slang changes quickly and thus the dictionaries will have trouble keeping up. There is, however, a sense that we have for our native languages that allows us to be able to construct words that others understand. Comedians are often very good at this. The two words you have offered from Chinese demonstrate this perfectly.

As a native English speaking American, I would express 学婊 by calling the person a "closet nerd."

This expression would not have made any sense 50 years ago and may not make any 50 years from now; but I guarantee every native English speaker (at least NA) would understand exactly what is meant by it. It is slightly tongue-and-cheek in nature as using "closet" implies that being a "nerd" is something to keep hidden from others. The derivation actually comes from being "in the closet" as a euphemism for being secretly homosexual. However, the modifier "closet ---" has taken on a life of its own and now may evoke sense of keeping some part of your life a secret or not fully admitting something about yourself to others, or even yourself.

Other examples of this usage might be, (New Yorkers will get this) a "closet Mets fan". Since the Yankees and Mets are both baseball teams from New York and the Yankees are overwhelmingly more successful, it implies, jokingly, that someone might "front" as a Yankees fan around coworkers, only to go home, lock the doors, close the curtains, and put on his Met's hat and shirt.

http://www.urbandictionary.com/define.php?term=Closet+Nerd

I don't think there are widespread English equivalents for those expressions that would be universally recognized, though you may find regional or historical equivalents. I wouldn't be surprised if the British have or once had words for these things, for example. That said, I just wanted to point out that "curve-wrecker" does have a negative connotation in the US. It is not a term of admiration.

I suspect there are distinct enough cultural differences between China and English-speaking countries, especially with regard to exams, that such terms don't exist beyond the usual ones like nerd or genius (which can be derogatory, like smart-ass). We do have insults like bookworm or poindexter (pretty slangy) which refer to people who study "excessively," but that's not as precise as academic overlord, which maybe we should just import into English! Overachiever is good as a general term for academic overlord, though it does also have a negative tinge, too, I think—can one really achieve too much?

Also, for the second one, we might use general terms of modesty but for your sense of someone who hides their real achievements, I'm fond of the term sandbagger, which refers specifically to someone who pretends they aren't as good as they are about something. You can use it in a variety of ways.

"Wow, you're really good at playing piano." "No, I'm terrible." "Stop sandbagging, you're awesome."

I wouldn't say it's universally known, either, but it's an option.