Methinks C would be a good thing to learn. Seeing that speed is one issue that might actually turn up one day, you'd have the skills to write modules in C ;) Personally, I'm attacking a problem right now that requires some C knowledge to go with me perl. That's a first for me personally. Thankfully I started as a C programmer.

As far as other languages, Java might not hurt for marketability. Not only that, but the similarities of other languages to Java would allow for easier steps to the rest.

Beyond that, I agree with some of the others here. You don't NEED to learn anything. But, where is the fun in that?