I think it might be Korean. But Maple Island is the same way. Some of the signs are in Korean. I thought it was kind of funny.
Not sure how you connected that to japanese, but I'm equally unbeknownst to other languages xD. It's korean, perhaps the source of all the updated wz files were raw from a korean client?
Oh sorry about that, I hope nobody got offended by me thinking its Japanese... It all look the same for me xD