The menus are in english somewhat and if you know how to play the game and want an easier time to relax you could try it if you could somehow get it. enemies hit far weaker far far weaker, less enemies in some areas, certain type of enemies dont exist in jp. all of your legions in jp cost about 1/2 up to 1/5th the price in eng to upgrade. bosses have more healthbars than jp in eng.
So basically eng normal is a harder version of jp hard with the same amount of healing.
speaking of healing items jp normal gets 9 small 3 large while eng gets 6 and 2.
the metal vs flesh system isnt as brutal in jp as well.
some enemies respawn in the eng version that dont in the japanese

there is no metal zombies in the jp version, they are the regular zombie swordsmen dudes.

this does effectively make eng hard sieg must die. in comparision to jp hard.

thanatos perfect requires 10 million exp vs the ridiculous 50 million in the eng release. as an example of the difference in price.