I'm having the same problem!
My site is 99% done, and its main language is portuguese. Everything is in portuguese, but I can't launch it because "Register" and "Cart" are not portuguese words.
It will be a multi language site anytime soon, so I would like not only to modify the text, but also allow these two words to be translated into other languages, using Joomfish.
I honestly have looked for hours, in all the files I could find, and I still don't get where to modify these two simple words.
Thank God I'm not the only one, I thought I was going crazy.
Tommorrow I'll try to do what teitbite told (I'm not in my computer), if xulen doesn't do it before me. But hey, teitbite, if you are also working in your own store with this te,plate, you could try to do it for us
And because this is the first membership post, I would like to say that Seichinha is lovely, he does a great job, and I want his autograph!