I agree Chinese or Mandarin is a much better language overall, but the author is asking which is better in ID?
If it is in ID you might like to consider what the country where the language is from is doing for our profession.
Japan has a strong and long history in design, and on par with much of the design though leadership in the west. It is a good place to learn, though much of their work is Japan specific with little exportability to the west, thought that is starting to change.
Korea, imho, is the place to go if you want to experience, a pressure cooker of design and fast turn around and low cost. Just look at where and how brands like Samsung or LG have come from and you can get the picture of where they want to go and nothing is going to stop them. However if you come from the west, there might be some cultural shocks in the way people work in Korea.
China, has a huge market, and lots of opportunities, but till now even though many companies and brands know where they want to go with design, but are not willing to take the risk to do so. Something is holding them back into true innovation. A Follower product strategy runs rampant in China, and designers need to ask themselves if that is what they want, or an environment they are happy to work in.