I need something to survive.

I'm thinking deeply over what language will be helpful for my future.

I have an awful time in terms of my business.
At last I get to know earning money is not easy.
When I was an employee, I didn't care about my monthly paycheck.
Because my company gave me a paycheck on an apponinted time.

I set up a start-up company with my friends 1 year ago.
In a depression it's not likely to be easy to stand all hardships.
So now I'm thinking about what to do for my future and business.

First of all, from a commercial point of view, Korea is small compared with China, Japan and the US. So there are more chances to get in China, Japan as well as the US. Secondly, Japan and China are very geographically, culturally close to Korea. You know especailly 2008 Summer Olympics will be held in Beijing, China. Definitely there will be lots of opportunities in China.

So I'm asking which language will be promising, Japanese or Chinese(Mandarin)?
I don't know how long it takes to master one of them.
Anyway, I should start learning one of them ASAP.