I don't know whether you can still appeal eBay's decision, but eBay's own item specifics did state clearly that the language was Japanese.
However, you offered a 30 day return so the buyer would have been entitled to return it anyway. The amount you would have had to refund the buyer would have been identical, the only difference is that you would not also have been required to pay for the return delivery.
Promotion fees are not returnable and the seller is always out of pocket for the original delivery cost, which has to be refunded.