Moving sdcard to ExtSdCard
thanks for upvoting this question but I'm afraid I still have no answer until this day either majority people. But let me share my latest research about this case which actually would be lame because I post this question pretty much long time ago. So, here it is.

When I do my research about it on the device, I try to root it, try to swapping the the storage and whatsoever (please notice that my Android's knowledge was not too much, so I think I may not trying all methods). It's all result nothing but pain and brick phone in the end of the day.

So I bring my phone to Service Center and after they re-install it I asked them about that case/issue, they trying to answer with 'not-clear-answer-to-preserve-reputation' answer, until I force them to spit the truth. Then finally they says that how Samsung Galaxy Ace 2 works. So, that's is, my last conclusion that this phone was made for experiment or whatsoever. I face this kind of experiment issue form Samsung not just once

So, I hope this story can brought us some unclear light to overcome the unclear darkness that coming from this phone (you can skip this last unclear sentence :p). Peace out :D