I'm pretty focused on Japan. There are other members of this forum who could fill in the blanks on other areas. Asia is a pretty large and diverse area, so it would be really hard to say one language would be better than another. It really depends on who you're targeting.
For instance, in [url=www.webmasterworld.com/forum32/18.htm]this thread[/url] I indicated that Japan has the world's 2nd largest online population. That's still true from what I've read recently, but it won't be like that for long. China will overtake everyone in Asia at some point.
Right now the Japanese market probably has more cash than any other. However, China because of the sheer size of its markets may eclipse that soon.
Woz also put together a great [url=www.webmasterworld.com/forum32/110.htm]Asia-Pacific: A Regional Overview[/url] that keeps getting buried, but is an excellent resource.
Due to the area of business, industrial electronics, Japan is a good option, but a near impossible market to breach for a company like ours as it, is the manufacturers HQ's, we have started gaining customers from china on an english .co.uk site. So Chinese is an option, though i may look towards Japanese
I will start another thread about the best languages or language for asia to get the biggest coverage within a cost effective framework.