Because Japanese and Chinese characters are slightly different, but Unicode decided to unify them under the same codes....
https://images.rpgsite.net/image/da49c9a1/102696/original/FF...
Ironically, they had a better Latin font _in the Japanese language version_ for all the genre loan abbreviations like MP/HP/LV etc., (https://terimaland.com/Memory/Steam_FinalFantasyPixelRemaste...) so that image is comparing the modded in Japanese Latin font vs the font the game includes by default.
(They also have a retro blocky "pixellated" font option iirc, which doesn't have the super narrow widths)
https://mailmate.jp/blog/half-width-full-width-hankaku-zenka...
Realistically it’s only katakana that you can make this mixup on. My desktop IME will let me type カタカナ or (reluctantly) ｶﾀｶﾅ, though it turns out iOS doesn’t have a way to type the half width kana, and IMEs have differing opinions on if they prefer full width digits, so you might see full width numbers like ５０００。