The process for account creation and checkout is exactly the same as on any English site. Common sense and Google Translate should get you through it! (They have a thing to translate entire web pages, don't they?)
Maybe not the best advice in the world, but the worst that could happen is that you put your address in a bit of a weird format, or you get lost before you complete it. Your card details won't even be accepted if you enter them wrong.
Granted, I probably wouldn't attempt to order from a website in a language I didn't understand. You could email them but would they accept a transaction via email? I guess you'd have to fill out the online forms one way or another...