FFX-2 International is really worth it, even though almost all text is japanese. You get used to it. And yes, the voices are english.

If you've got north-american FFX then you probably don't have the dark aeons and penance included, which ARE included in the PAL and INTERNATIONAL versions. Int. has also a cutscene called "Eternal Calm" which is a hint to FFX-2

But Final Fantasy X-2 INT beats the original FFX-2 by far. First of all, there are two new dress spheres, Psychiccer (Saikikka) and Festivalgoer (Omatsurishi). Psychiccer is a nice DS with element-eaters as passive abilities, a death-like ability called Telekinesis and a semi-useless Teleport ability. Also, it is ranged, and Yuna's Festivalgoer DS has two attacks like thief. Then, Shinra has completed his latest invention. Have fun with it, as you can capture fiends and put them in your team, fight cups in the colliseum to meet Major Numerus, which has 2.666.664 HP and gives, if you're really lucky, 20 Iron Dukes when defeated. Well, there are a lot of other changes too (Trema has spellspring, for example) but I won't list them here.