Postdoc in China: what are the possible difficulties and disadvantages?
I'm doing a postdoc in computer science at Nankai University, Tianjin, China. You've asked about the negatives, but I first want to point out that I love living in China (my friends talk about how they should visit China one day; I live here!). It's not perfect, but it's not nearly as bad as made out on Western media. And I feel physically safer here than I do in any other country.
Some items that might be of concern:
Culture shock. Have you been to China before? Because wow! It's a shock when you're new. I recommend visiting (e.g. for 3 months) before taking up a job here. Things you'll need to get used to: chopsticks, squat toilets, pollution, crowds, haggling, real Chinese food, the great firewall (e.g. Facebook, Google, Dropbox are blocked), crossing the road, finding clothes that fit, fighting over the bill, people pushing in front of you, traffic. A lot of the time, you won't really know what's going on because it was explained to you in Chinglish. At other times, things won't make sense because they're just done differently in China.
Low salary (by international standards--well paid by Chinese standards). But the university should cover accommodation (so no bills to pay), and cost of living is next to negligible (as long as you eat the local food; Western food incurs Western prices).
Language barrier. Even if your colleagues all speak English, you will need to do things like buying food, taking taxis, etc., which will require some level of Chinese (unless you want to disturb your colleagues repeatedly). You might end up misunderstanding important things (e.g. your salary level) because it was explained to you in broken English. Also, how good are you at pronouncing Chinese names (your future co-authors names)?
Medical care. Forget having privacy; expect to explain your medical conditions in front of maybe 5 other patients. Oh, and probably one of your work colleagues will need to translate for you, and help you buy medicines. (It helps if you know someone who's a doctor.)
Loneliness. All of your friends will probably be through work. They will go off and spend time with their family and friends, or go back to their accommodation, and you'll be left alone. You'll be a kind of outsider, and people might be too shy to invite you to events, even though you are lonely. (From my perspective, this is the worst aspect of living in China.)
Proofreading papers. You're probably going to get asked to proofread/polish a whole bunch of papers.
Administration. In order to get a work permit, there's a lot of forms to fill in. You'll need a "foreign experts certificate", a "work certificate", and there's a medical check and an interview. Many forms will be in Chinese (and your colleagues will likely need to fill these in for you).
Grants: There's also special grants for foreigners: Research Fellowship for International Young Scientists (which I'm on currently), and the 1000 Talents Program.
No fixed address. When people ask me for my address, it's hard to explain to them I don't actually have one. (E.g. I'll stay in some random hotel for the next few weeks, then I travel to some country, and will stay in some other random hotel.) I essentially live out of a suitcase.
Hard work. People in China seem to work much longer hours than in Western countries. (E.g. I'm in the office virtually every day, including weekends, from morning to night.)
Team work. China is the country of people power. Everyone in our lab helps out everyone else, and we end up with papers with many authors.
LGBT? Don't be too obvious about it and virtually nobody will care.
Religious? For my postdoc, a government official told me that it's okay to have and practice a religion, but not to preach religion. (Easy for me; I'm not religious.)
Vegetarian? It's tricky completely avoiding meat; it's easiest to just accept that you'll occasionally end up with meat. (You'll probably need to get used to tofu and spicy food, if you're not already.)
Woman? Expect groups of men (typically construction workers and gardeners) to stare at you, making you very uncomfortable. Also, some Chinese men will think of you as "exotic". (Oh, and I can't find anywhere to get my eyebrows tinted.)
Man? You'll probably be requested to drink (lots) at celebrations, dinner meetings, and so on.
Bathrooms are disgusting. Knock before opening the stall door (if there is a door)---it most likely doesn't lock and if you open it without knocking, you might interrupt someone (and you need to say "you ren" = "has person" if someone knocks on your door). You'll need to get used to squat toilets and carrying around your own toilet paper.
People are less uptight about things. E.g. people will compare skin colors; males will have pictures of sexy women on their computer; movie and software piracy is not a big deal (even on the lab computers). Things that are not really appropriate in Western countries.
Other things: Random people will take photos with you (or of you). Fresh milk is difficult to find. Coffee is poor quality and expensive. It's hard to get decent wine. Don't drink the tap water.
The things you ask about (but I don't have a general answer):
Collaborations. It's a bit embarrassing having to ask for letters of invitation from colleagues. Other than that, it's been real easy for me to travel.
Conferences. It's easiest for me to go to conferences as the professors are too busy, and I don't need a visa for most places. I travel a lot.
Duties. They're trying to make me associate professor here; which will require teaching a course. I have no idea how I'm going to do that.
Attitude to scientists. Held in high esteem, although you might be mistaken for a foreign student if you're young looking. The public won't be able to understand what a "postdoc" is, though (it's easier to say "teacher").
I know this question is dated thus likely the OP Artem has finished his/her Postdoc contract long ago. But I will leave some comments as well, as a westerner (from a 3rd world country, engaged to a foreigner) finishing a 2-year-old postdoc contract in South of China.
Rebbeca's answer above is quite complete and fills most of the points, however some aspects may change depending on the local institution traditions and the candidate's background. This is why I emphasised the where I am in China and the fact that I come from a western 3rd world country, along with marital status.
Pros: China has great food, fantastic scenery, rich and deep culture and knowledge. Thus life in China will be anything but blend. Still nowadays a foreigner attracts considerable attention and interest, thus there will always be someone willing to help and get friendly. Academics are very respected in Asia, thus a postdoc should expect cordiality and polite treatment essentially everywhere. Criminality is almost zeroed, especially against foreigners. Stealing is rare, and people are relaxed about taking care of their belongings. In spite of officially a dictatorship there is a lot of individual freedom in China, as long as one is no activist. Likely the greatest positive aspect for a postdoc, getting a job in China is currently quite easy for anyone willing to embrace the culture, particularly open-minded foreign PhDs.
Cons: Local culture is not open nor flexible, meaning you are expected to accept local ways all times and gradually conform to or adopt the Chinese way of life. This tends to overwhelm foreigners so that most end up living in an expat bubble and eventually leave. As mentioned, salaries are usually lower and quite often there is a catch behind salary discounts. Communication is a major issue not only because of language barrier but actually mainly because most people in Mainland China imply statements and suggest contexts instead of uttering their minds directly. Assertiveness is often perceived as arrogance and blunt statements can easily offend. Because of their unique and inbred culture, Chinese nationals get easily offended (people say they are "glass-hearted") and in the counterpart cannot understand/accept what could offend a foreigner. There is a strict hierarchy in almost any form of communication which is hard to abide to as a foreigner with a democratic mindset. Scamming and lying are quite common and culturally acceptable depending on the context (meaning quite often others will not have you complaining about it). Face and clan cultures are not easy for just everyone to swallow. Local work culture pressures on posing all times, thus locals will pretend to work literally everyday from early morning into the night, and will post hardworking-related status updates on social media... even if they do not really work much. The internet feels like Truman's Show and workarounds are unstable, troublesome, and expensive.
I will quickly summarise what makes me very happy in China and what drives me nuts. I feel in heaven while eating and shopping as prices are low, variety skyrockets, and quality is overall quite good. I feel physically safe at all times as long as I am wary of where I thread. Finding solitude isn't hard and I can have a mind of my own. Nature is still here and looks beautiful. The written characters are gorgeous, the language doesn't sound too bad, in every corner there is something new to learn. My friends are reliable and always willing to help, and I want to keep them forever. The concept of social peace is central to Chinese society, thus conflicts and uncomfortable situations are avoided whenever possible. I feel growing quickly as a person and culturally. Clearly the country is developing at unrecorded speed through adopting strategies which are unknown to most foreign governments.
I get desperate and think of running to the airport every time I find myself unable to send/read an email or paper, or the Skype call won't work. I bought a local LeNovo computer which turned out to be a nightmare because of language/system/connection settings which refuse to be changed plus a patchwork of hardware issues still surfacing. In the lab most of the time I feel frustrated and baseline angry because I cannot easily make myself understood in too many different areas (requests, reasoning, questions, acts, etc), resulting in my generally avoiding communication. [Trivial examples. There is no equipment maintenance, nor routine of cleaning and organisation; nobody cares. Details which are usually not important: statistics; concentrations; temperature & humidity conditions; precision; light:dark regularity; brands; purity; reproducibility; authorship criteria. Nobody is responsible nor knows about anything unless when given an order.] I have had payment conflicts from the day of my arrival, and of such complexity that would feel a monograph -- at the end I hope leaving in a civilised manner with at least 80% of the agreed salary. I am never comfortable, be at home or at work, as rooms are generally cluttered and dirty (all shared) with some degree of structural damage and pests are a constant nuisance. (Mosquitoes, cockroaches, sometimes a rat.) Authorships are locally exchanged like handshakes, and my adamant refusal to join in the club has generated tension also from day 1. I must add that advisors/supervisors see themselves as emperor thus expect being covered in flattery and papers from just sporadically sitting at their desks/thrones. The university administration has provided null help for any official procedure, including translations and health/police certifications (they didn't know what should be done or where), and they will not have me asking them questions about unstable salary pay. Finally, I mentioned my friends are gold, yet jewels are indeed rare: almost everyone approaching me is openly seeking language favor, authorships or marriage, and that might get delicate when involving some expectation of a hierarchy.
I believe some of the mentioned aspects are highly dependent on circumstances, as follows: I believe US citizens (normally given top VIP treatment in China) and Europeans would have no issues with salary pay nor quality of accommodation; Western provinces or regions near Mongolia are regarded as not so safe; faculty administration is said to be more professional in the most highly developed centres such in Beijing, Nanjing, Hangzhou; there is a strong stigma against anyone who does any drugs excepting alcohol; aggressive/impolite types may find it harder to make friends and adapt; someone willing to marry a Chinese partner will culturally and socially adapt much more smoothly.
Sorry if too long. I hope my description enables someone to decide whether China is what they are searching for. I would have greatly appreciated reading about these points before coming -- I would have not decided otherwise but would have taken many specific precautions.