It is difficult to say which Asian language you should learn for business purposes. Any Asian language will be a huge plus in your CV. But I would suggest to you that you either learn Chinese (Mandarin) or Hindi, because those are the Asian languages that are spoken by most people. On the one hand you should learn Chinese because it is the most spoken language in the world (even before English!), but on the other hand you should learn Hindi because, as you already said, their economy is booming. In the end it really depends on your aims and where you want to live or work and which language is better for that purpose.