chinese

I'm not an expert, but Mandarin is statistically the most used language in the world. And China is growing.

If your career target is a multinational company, neither Chinese nor Korean should you focus - you should focus on English. I've been working with some multinational companies after graduation, for example, IKEA, MGB Metro, Carrefour etc. The majority of those employees are Chinese, but English is their working language, i.e their documents, computer systems etc are all English. You won't have any problem if you can speak English. Chinese or Korean, I think it's only optional and won't make big difference. However, if you are serious about learning one of them, try to ask yourself which country you are able to be connected with.