Which languages (besides Spanish and English) are in high demand, or useful, for business?
Background: I'm a native Spanish speaker from Puerto Rico whose fluent in English and speaks Russian at a conversation level.
Depends on the place where you live, though. As I don't know how the situation is in Puerto Rico, I can't really comment about it. Also, it depends on the field you work in. For example, I'm a student of Food Technologies and would find, say, French or German useful since it opens me door to investigations on the food industry (these two are the most important languages in this field apart from English, I believe). I know for sure French and German are very useful regarding scientific texts. Other than those ones, I couldn't know less. ALSO: In my opinion, the less learners a language has, the higher its offer-demand relation is. Millions of people learn English, so it doesn't put you in a high place, but not that many people learn, say, Polish or Hungarian.
I've heard Russian translators are in high demand, and that many sources of engineering-related information are still only in German. However, for such an important decision, you should probably do a lot of research from many different reliable sources (sorry I don't know any to get you started).
Computer programming languages...
Most would say China, I disagree they are not in a strong position, yes you certainly could do just fine learning that language. However companies are going to start to pull manufacturing back to the States; U.S. recent tax breaks are staggeringly significant. China immediately lowered their corporate tax rate to 0%... zero that how bad the situation is.
English has you covered as the language of business; Spanish some nations in South America are going to have strong emerging markets. Investment confidence is growing as nations are rejecting the socialist tide that just a decade ago folks thought would sweep South America into the dark ages. A terrible mirror was held up in Venezuela; that mirror showing the promise vs the reality of what socialism brings might have saved the rest of South America as recent elections show.
There is a reason I’m learning Spanish, watch how quickly things change the next decade. If South American nations can resist the communist push the sky is the limit. China and Europe also Canada if they continues on the collision course with disaster will all be replaced by South American nations as the U.S. main trading partners.
English and Spanish is the way to go. Portuguese also a good choice but that's more all your eggs in one basket kind of choice.