I've talked to lots of PHP and Java programmers who love the idea and concept of Rails, but are afraid of stepping in because of Ruby. The argument goes that since they already know PHP or Java, that it would be less work to just pick one of the Rails knockoffs in those languages. I really don't think so.
Ruby is actually an amazingly simple language to pickup the basics on. Yes, there's a lot of depth in the meta programming corners, but you really don't need to go there to get stuff done. Certainly not to get going. The base mechanics of getting productive takes much shorter than you likely think.
After all, Ruby is neither LISP nor Smalltalk. It's not a completely new and alien world if you're coming from PHP or Java. Lots of concepts and constructs are the same. The code even looks similar in many cases, just stated more succinctly.
Learn Ruby in the time it would take to learn a framework
I'd argue that most programmers could get up and running in Ruby in about the same time it would take them to learn another framework in their current language anyway. I know it sounds a lot more scary to learn a whole new language rather than just another framework, but it really isn't.
The number one piece of feedback I get from people who dreaded the jump but did it anyway is: Why didn't I do this sooner?
Learn while doing something real that matters to you
Also, speaking from my own experience learning Ruby, I'd actually recommend trying to do something real. Don't just start with the basics of the language in a vacuum. Pick something you actually want done and just start doing it one step of the time. You'll learn as you go along and you'll have to motivation to keep it up because stuff is coming alive.
So don't write off Rails because you don't know Ruby. Your fears of starting from scratch again will quickly make way for the joy of the new language and you'll get to use the real Rails as a reward. Come on in, the water is fine!
See the Rails Myths index for more myths about Rails.