If you definitely need to use R, I'd say just learn R. R is different enough from most other languages that I don't think you'd get a lot of value from, say, learning Python first.
Why do I say that? First of all, R's syntax is quirky and different enough from (Python|Java|C|Ruby|etc.) that you might almost find it harder to learn R if you're already used to something else. Second, aside from the syntax the biggest thing to get used to with R is that it's very much vector oriented. Basically you're always working with vectors, even when you only have what you would otherwise think of as a single scalar value. You just put in a vector of length 1. Anyway, that whole paradigm is different enough from other programming languages, that you might as well just learn it that way from the beginning.
Now to be fair, there are libraries and things that let other languages act and feel a bit more like R, but I'm intentionally not considering those right now, as that would just be one more complication to deal with. And if you are locked in on using R for whatever reason, there's no need to complicate life.
The only other question I would have, is whether or not you absolutely must use R at all. If you have the option to choose your language, you can do pretty much anything that you can do in R, using Python, or Octave, or probably many other languages. If that's an option, then you just need to decide which would be easier / more useful for you. And while I won't take sides in general, I will say that Python may be a little bit easier to learn in general, but then you're back to using external libraries for more of the statistical / numerical stuff.
Just looking to see if I could learn R without knowing much else.
My guess is that you can. R has some quirks, but there's nothing especially scary about it. Depending on how much you already know about statistics, you may find that learning and understanding the math is more difficult than learning to use R.