I've often said that English is to programming as Latin is to medicine. Programmers will be writing "if" statements and "for" loops long after no one uses "if" or "for" in daily conversation.
So it is as important for programmers to understand English as it is for doctors to understand Latin. Of course, most doctors may understand Latin, but they wouldn't be able to converse in Latin. In that sense, English is also the programmer's lingua franca.
That term -- lingua franca -- is an interesting one. In addition to being used as a colloquialism for "a common language" it was also, itself, a language: http://en.wikipedia.org/wiki/Mediterranean_Lingua_Franca . Just as Lingua Franca eventually took on a life (and grammar and vocabulary) of its own, I expect "hacker English" will, over time, do the same. In fact already my (English-speaking) wife thinks that I'm speaking a foreign language half the time when I'm talking with colleagues over Skype.
It's less important to know "English", and much more important to speak, converse, and communicate with other hackers using the lingua franca of the day.