A lot of your real-time software will be developed in C/C++, though, as Wayne said earlier, Java is becoming a bigger player in these fields (as in FIRST Robotics). The real answer to what computer programming languages to know is all of them ;)
Different languages have different features, and different areas in which they excel. Knowing C/C++ and Java is a great start for almost anything in the Computer Science and Robotics fields. Knowing Python and Perl are useful no matter what you do. And if you know older languages like FORTRAN or even COBOL, you have an in-demand skill that few poeple can match.
The great part about programming is that once you understand HOW to program, a new language is just another challenge!