I try for days to unpack them, but I can't .... You can try this, it uses yu-ris engine.
The game will be ported to steam too, so the engine will be unity (probably). So what can do is take the r18+ text and translate it and once the game is out put it in along with the cg. Or do the opposite, take the English text and put it in the Japanese version. You need someone ace in programming overall and translator.