Japanese (or other language) version OS X

Hi, I live in Japan and I'm about to buy a new PowerMAC G4 (1 GHz). I have already seen the Japanese and English versions of MAC OS 9. To be able to use the English version, I have to erase the Japanese version and install the English version. I want to know if this is also true for MAC OS X. I believe there is only one version of OS X and I just have to go to System Preference-->International, then drag the language that I prefer on top of the list. I was thinking why Apple Store Japan is offering Japanese and English versions of MAC OS X (same price) and other retailers here don't. Does MAC OS X come in different language versions?

Thanks in advance for any input.