I think English is a "must learning language" now, because if we can't speak (or at least understand) English, there will be so many things that we miss. Like indonesiaindonesia said, most of the information stored in the internet is written in English. So, if we don't wanna be left behind, we must really learn English as our second language.
As for the other languages, I think I'm also interested in learning Chinese, though I 100% agree that this language is hard to learn, but it's quite interesting. The tones, the characters, and not to mention the variaty of the language itself, such as mandarin, cantonese, hokkian, etc. Ooohh ... so complicated... hehe ..