He mentioned picking up Mandarin in one of his Ars posts, I think. Not "fiendishly" clever, just apparently more clever than the folks running our intelligence services.
As Confucius said, in one of his most famous take-downs, "始吾於人也、聽其言而信其行、今吾於人也、聽其言而觀其行。At first in dealing with people, I would hear their words and trust their deeds, but now my way of dealing with people is to hear their words and observe their deeds." We'll see what appears about his planning and his view toward China and a lot of other things about him as he continues interaction with news media and the governmental authorities of various governments.
Sorry, if it sounds personal but I have to ask: How do you know he's not proficient and what does your proficiency have to do with it?
I have a basis of knowledge about how language proficiency is defined (the federal government in the United States has a standard rating scale of foreign language proficiency, as do most other countries with an active diplomatic corps and military alliances with other countries) and I know how much time it takes in specialized training programs and in-country to become proficient in Chinese, none of which Snowden has. I would find it more believable that he has some knowledge of Japanese, because Snowden lived in Japan for a while, but he apparently has little knowledge of that language either.
wow. Err... aren't there other ways how to learn a language than government sanctioned programs? How about attending lectures in the evenings and a Chinese speaking friend (not that unbelievable in Hawaii).