It's an issue of limited space for English text. This game has only SJIS encoded characters (i.e. 2-bytes, double-wide). There is no half-width Latin font sheet. This results in too little space in existing memory (or screen real-estate if using SJIS) for English text to result in a meaningful translation of each line of dialog. There are a few options to remedy this:
1) Modify the story script files' pointers/offsets so that each line of dialog ends/begin at a custom location in memory, which will still result in a very large font (visually) but would at least allow for the fully translated text to be present (
EDIT: this would be achieved with additional pagination when dialog text is displayed and cycled).
2) (WARNING: bad solution) Modify the font sheet so that every combination of two Latin characters (side by side) is present, overwriting the original katakana/hiragana/kanji, which is only an option if A) enough Japanese font tiles already exist to fit those letter combinations and B) the font sheet is even accessible, which I don't believe it is, as I believe this game uses the BIOS font.
3) Create an entirely custom font sheet with each letter of the English alphabet, along with all necessary punctuation, and then modify the game to use that font rather than what it's using now.
All three options are tedious, and so far I believe #2 to be out, as the game seems to be using the BIOS font and not its own font that it ships with. I've looked into #1, but not that deeply. I believe this game to function similarly to SEGAGAGA in regards to its font, which you can see megavolt85 talking about here (keep scrolling down and continue to page 5 to see more progress/explanation)
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