Can a .3dz for one region (US) be played on a 3ds of another region (Japan)? Or are .cia files the only way to play a game for a different region? Can .3dz be converted to .cia, is there anything else needed to be done in order to work?
Yes, Monster Hunter 4G (JPN).3dz can be played on a US XL. You don't need to convert it.