I'm on the same boat as you. They charged me a day after I preordered the JP version (at end of September). Switched to Chinese/English version. What they do is deduct what they already charged you for JP version, off of the Chinese/English version cost. In my case, $83.80 CAD was my cost for the JP version and $83.50 for CH/EN version. They didn't charge me a second time (i.e. didn't claim the second payment through PayPal) and put the $0.50 difference as store credit. Hope I made some sense... Click on your order, go down to invoice and check your payment amount (should be the JP amount), then less the order cost (should be CH/EN cost), and then you should have some outstanding balance.
I wouldn't be too concerned for those who haven't been charged yet, but it's probably safe to follow up with their customer support to make sure you get the game on time! An order I made with credit card in the past was also not charged until shipping date.