This is a really great project. I'm glad someone finally picked this up. I never liked the j2e translation, the font is horrible, the text boxes are oversized / looks ugly, and there is this swearing all the time.
I like that this is an edition of the american Final Fantasy "II" release, because this version doesn't need hours of grinding. Who still enjoy this, seriously ?
However I have to say something. It's a great idea to use the "ll" and "il" idioms for "Cecil" and "Tellah" but you should also use them in the game's text. You could also use idioms for "ill", "ili" and "lli" as in the FF3 translation. (only requires 4 additional tiles : i + half a l, l + half a l, and half a l + i, half a l + l)
Also I think lines starting in "Soldier A:" are hard to read. I don't know why buy they look strange. You should probably add a quote after the ':', or at least a space.
I wish you best of luck for potential future updates of this project.
And, by the way, yes the FF4A version of the game is very slow. Even moving your cursor in menus in slow in this version. However it has nice translations in many languages, the graphics are updated, the game is still very close to the original, and there is my awesome sound restoration patch. The main advantage is that after playing it, going back to the original makes it feel very fast, even on a PAL console.
Fixing the black magic icon bug is theoretically possible (by dynamically placing a black tile on the background when this window show up, and then placing a normal background tile again), but it's probably not worth the trouble.
Note that the same bug appears every time you find an item with an associated symbol in a chest, and it's present in the equip menu itself too.