If you're worried about your Chinese withering away, you should definitely study abroad in China (e.g., Shanghai).
If you want to go to a different/interesting/pretty city, study in Kyoto. I've met folks who studied at Kyoto University. There's a tech industry there, since Nintendo is in the area (and small game startups have grown up around senior folks who have left Nintendo). Or you could live in Tokyo or Osaka (big cities with tall buildings).
With classes in English but really solid technical courses, you might want to consider one of: Budapest Semesters in Mathematics Aquincum Institute of Technology Math in Moscow
The first two programs are both in Budapest, and the second one focuses on computing while the first one is (obviously) more focused on mathematics. If you have a theoretical bent these are good choices.
I spent a month traveling throughout Europe this summer after graduation- it really is so easy to travel about in if you want to see a lot. This would be a list of cities I try to study in (obviously depends on the program you choose) but you can't really go wrong with any: 1. Zurich / Rome / Prague 2. Berlin / Amsterdam 3. Paris / Budapest
Come to Israel. You can meet world class professors at Tel Aviv U, Hebrew U, and of course, the Technion in Haifa. And check out: http://mappedinisrael.com/ for a list of startups in Israel.
This is a mostly a case of personal taste, isn't it? :P
I would love to travel to both Japan and South Korea, but I'm sure they're not for everyone.
I'm a little biased but I'd say buenos aires :)
Analogy:
>If you ever do find yourself working for a startup, here's a handy tip for evaluating competitors. Read their job listings. Everything else on their site may be stock photos or the prose equivalent, but the job listings have to be specific about what they want, or they'll get the wrong candidates.
>During the years we worked on Viaweb I read a lot of job descriptions. A new competitor seemed to emerge out of the woodwork every month or so. The first thing I would do, after checking to see if they had a live online demo, was look at their job listings. After a couple years of this I could tell which companies to worry about and which not to. The more of an IT flavor the job descriptions had, the less dangerous the company was. The safest kind were the ones that wanted Oracle experience. You never had to worry about those. You were also safe if they said they wanted C++ or Java developers. If they wanted Perl or Python programmers, that would be a bit frightening-- that's starting to sound like a company where the technical side, at least, is run by real hackers. If I had ever seen a job posting looking for Lisp hackers, I would have been really worried.
If you're on HN and state plainly that language is no obstacle, I assume you have an interest in meeting driven, energetic individuals like yourself. Whether that's because you're interested in meeting others who will help you grow intellectually/emotionally/spiritually/etc. or because you're interested in meeting the Larry to your Sergey will help guide your specific choice, but either way you'll be able to apply the above principle. Whatever you do, pick a place with high barriers to entry. How high? What kinds of barriers? Depends on what kinds of people you want to meet. If you want to meet other students who, unlike yourself, were unwilling to learn a new language, study abroad in the UK or Australia. If you want to meet some ballsy-ass motherfuckers, study abroad in Shanghai. Etc. You get the idea. (Really though, I met a couple who just came back from 3 years in Shanghai, and they both said anyone and everyone there who spoke native English was somebody worth getting to know.)
This isn't to say there won't be many, many other factors involved in your decision. Certainly, all other things being equal, cities with tech industries are preferable to cities severely lacking in tech, cities with angels/VC's are preferable to cities without, etc. But if you just weigh things like that, you may as well "study abroad" in SF, no?