The unfortunate thing about this game (I've already finished it and can't be stuffed playing it anymore) is that you have to just play it in Japanese while dungeon crawling, cause it keeps freezing up during monster battles.
You can switch the language in the game before a battle starts, and you should be fine.
I can "finish" the game in English with the patching I did and posted. But I had quite a few problems, like Olivia's sex stats didn't update after her events; ending list after last boss doesn't have harem, Olivia or best end; game crash at 1st battle in NG+ (but can be played in JP with same save).
So from what I've seen, I think the dev only tested throughly for the JP part. The other languages only got tested for the trial, or didn't get tested enough after adding the DLC parts. That's why the game still can be played through the lower 3 floors in other languages, but all later monsters had wrong image file links in the translated data files, causing the crash, and Olivia's wrongly using Rii's battle image. Likely the translated scripts for story/dialogue don't set the right flags for the added contents from the DLC too.
In the end, this game (or at least this version) can only be fully played in JP. Even if you use my patch, you'll likely have problems down the line. I think you can play in JP to unlock the events (or just use a full save), and read the memories in English if you want to.