Thank you for pointing these things out. We'll take them into account for the final game.
For the voice over we are planning to hire a professional voice actor (in native Japanese). The voice of the demo was done by ourselves as the budget didn't allow to hire a professional yet.
As for the language used, we will review it for the final game and we will make changes to be accurate with the history period. Very well found, we didn't thought on that, thanks! :D