I lived in Guangzhou for a couple years, recently moved back to the valley. Passed 5/6 levels of language certification, was enough to communicate with co-workers and deal with my projects and get around.

The biggest obstacle I found was that often my ability to communicate with someone had less to do with my level and more with the person's preconceptions of "foreigners". So there would be some people where I would speak Chinese and they'd have a stunned "Whoah, a talking giraffe!" reaction, and with others it was totally normal and fluid.

The concept of "internationalization" as it exists there is "more people should learn English to communicate with the outsiders", not the sort of melting pot ideal in the US.

Chinese do not distinguish between race, nationality, and language, they are all one thing. It is for some reason inconceivable to 99% of people that any (white-skinned) foreigner could learn Chinese, even though most of us do. Whereas it's a real head-scratcher for them if, for instance, an American of Chinese ethnicity who grew up only with English came to visit and didn't magically know the language.

There were many situations where I found myself excluded from things or where people refused to communicate with me directly at all about things that concern me, which may be as much language as cultural.

So I'd say learning the language is a good investment if you spend any period of time there, but being of non-Asian ethnicity will be a giant road-block to any real sense of integration, in spite of overcoming the language issues.

A few months to get good enough for daily stuff and short casual conversations. A couple of years for work meetings with friendly colleagues. Much longer to be able to deal with negotiations with outside parties.

It requires significant and sustained effort. Most people stop studying when they're ok with the situations they care about. What level that is depends on the person.

If you are considering Beijing, don't worry that language will be a problem for everything. But many things will be a lot harder. Selling to Chinese businesses and consumers is the obvious example. Many foreign-run companies sell to foreigners or foreign-owned businesses in China.

I took a semester in 2002 of intensive mandarin at PKU just for fun, and it has gotten me by for the last 9 years working in the Chinese branch of an large Redmond software company. Most foreigners do less chinese than me and still get by.

Of course, you'll miss a lot of the open office chatter, negating the point of that, you'll get uninvited to meetings that they want to hold in Chinese. Microsoft is worse than this than other foreign companies, my Chinese wife worked for SAP which had more foreigners and less language issues as a result.

But there are plenty of reasons not to come here beyond language, and a few to come if you are at a restless point in life.