How playable is it if you can't read Japanese?
It's at least -somewhat- playable? In reality you'll chances are be unable to get the 'Best' ending (as this requires you to do a few key events around the world map in a single run) but you -should- be able to get from start towards an eventual finish easily enough.
As for the different endings:
-Jeanne's Victory requires you to find the Vampire Queen and defeat her.
-Chris Victory requires you to find the mask breeder in the corrupted underground and defeat it.
-Charlotte's Victory Requires you to find what is more or less the Goddess' realm, and win a final duel vs her.
-'Everyone's Ending' requires you to find the Consuming Darkness via one of 3 secret paths (Ether learning such from the dragons, unlocking all other portals to take the upper passage, or via the ice kingdom's subplot) without doing all 3 subplots to unlock the route towards it, and defeat it.
-'True Ending' is more or less the same as the other, but you did everything else first.
As I said in my first post, you can KINDA run into the boss events for each of these and then end up beating the game as a result. All but 1 can be just gotten by exploring areas and activating events left and right. IF you don't plan to use the Goddess' cheat room, just checking off everyone's crystal events on the maps is a good way to get special gear, mentality's, and other such goodies. The game's also got an 'extra reward' for those who can beat it without dying once, but honestly if you don't care about those silly end game achivements you can just after getting an ending force unlock everything and enjoy stuff at your leisure. The only things is that seeing the True ending can only be seen by doing it, you con't get a chance to view that version from the gallery (BTW, Jeanne's Ending is on the left, along with her monster events, while the other 3 are on the RIGHT, along the other global events).