https://w.atwiki.jp/dq_binary/pages/31.html
Thanks! Alas, there's not a lot of information on that page, and all the links I tried are giving me 503 errors, so I can't even try it any of it out for myself

. Assuming they actually do have a (non-Overworld) map editor, I'm curious to see how well it works.
Oh and abw, I'm really sorry, I'm trying to update my DW2 rom with your latest Menu Upgrades patch (via asar). I must be forgetting something (it's been a while) that's different in my ROM compared to an unchanged ROM but I'm getting a glitch when I try to buy any weapon/armor in a shop (It just skips the party menu and goes straight to the "(Cannock) Can not equip this are you sure?" message and the graphics glitch out,
Probably what you're missing are the 2 new menus and their pointers. Basically I just took the 2 BUY/SELL target menus (from pointers #18 and #42), copied them to new menus (creating pointers #75 and #76, which meant shifting the entire block of menu data down by 4 bytes), updated them to include a space and the new optional E control code ($F0-$F2 depending on the hero), and adjusted their size/position to fit the new text.
Why do you need multiple lines for one line of the window? What are the spaces for?
Because it's not one line of the window, it's two lines divided up to match PPU attribute boundaries so that the game can apply the right palette when clearing and drawing the overlapping tiles (of course, the palette doesn't change between the parts of the COMMAND and EQUIP menus that overlap, but it's all part of the same system that handles rolling the EQUIP menu up and down over the map background which almost always does use a different palette, so the overlap section still has to obey the same rules). A tiny bit of experimentation will show you that that "AN " is the "AN" of the top line and then the 2 spaces on the second line directly under the "AN". The rest of the data works the same way, e.g. "SP " covers the "SP" on one line and the " " directly below it.
After updating that section of data, you'll want to test getting into a battle, because despite being completely separate conceptually, the game actually uses one of the strings of 4 consecutive spaces from that block of COMMAND menu replacement text as one of the black backgrounds in battle

.
And yes, DW2's menu clearing/redrawing is indeed a pain.