Language Study: What is a foreign language worth?

Sort of. More precisely it refers to the artificially standardized accent derived from northern Chinese that the Chinese government tries to have everyone in official positions use, and broadcasts to the entire population of the country through radio, television and education systems. Whether anyone at all actually speaks it off-air is another matter.

If by Mandarin you mean spoken and written Simplified Chinese, of course, that would be difficult.

I didn't mean that at all, but I do read/write/type.

Many Chinese students have to struggle for a decade on it, too, not to mention the required ancient Chinese in textbooks.

I also read some ancient Chinese, in fact I'm writing a history book about Yunnan using not only ancient Chinese but other language sources (Burmese, Tai, Tibetan, etc.).

Programmers in China are more or less capable to at least read documentations in English, some may even have skills in writing and speaking.

This is all beside the point... programmers everywhere have those skills.

I have heard that learning German language is less paid off because Germans are just damn good at English that they do not always need a German-Chinese translator/interpreter but talk in English during a business conversation.

And this is a tangent. Well, thanks for your input. I'm not sure that I understood it properly, but you seem to have essentially agreed with me.

Because I am not going to discount a skill someone might find valuable, even if it's only by oft-repeated social wisdom and never borne out in practice.

Your argument is true in the sense that it's impossible to disprove. However, it's pretty weak. Generally, if someone hires you with an interest in your language skills, they will at least mention it in the interview.