CS4 English International vs English US

Where can I find info on the difference between installations of "English-International" and "English-US"

When I go to install CS4 Premium, after putting in the serial number, and clicking "accept", the next screen that comes up has a grayed out box that says "English, International".

If I go "back" and select to install as "trial" version and go to the previous, (the next screen after "accept" license), I have options to install as "English-US" or "English-International".

I stopped my attempt to install until I can resolve this issue.

I could attempt to install as trial "English-US" and then after install, attempt to activate with the serial number, but I hesitate to do this.

Please advise asap. Please direct me to Adobe tech info on the differences of the two versions.

Thanks,

RPP