Why is the Japanese Booster Box for Obsidian Flames so much cheaper than the English one?

I'm somewhat new to this, which is why this might not baffle others when I'm pretty confused at this.

On a card store site, I saw that the Japanese booster box set for Obsidian Flames was way cheaper than the English booster set. The Japanese set was 65$, while the English set was over 200$. I can get why the English set is at that price, but why is the Japanese set so cheap in comparison?

And I'm questing to get the Charizard EX Special Illustration Rare, I don't really care what language it's in, so what's my best bet here?