I think I get what you're saying about translating the descriptions and flavor texts!
Just to be sure though, I'd like to list the key takeaways I'm getting.
Essentially, each girl card has effect text and flavor text string variables, some of which correspond to different difficulties, and they're written in a similar way to how &イージー効果テキスト (Easy Effect Text) and &ハード効果テキスト (Hard Effect Text) are written in files like the 300## card.txt ones. Unlike the 300## card files though, the comparable string variables for girl cards don't appear in their texts files, but are instead stored elsewhere, likely within the Unity code. I can still create translations by writing those earlier mentioned Japanese string variables into their Japanese card files and attaching a translation to each variable in a similar way to how having "&カード名,Master Konoha" in her Japanese file translates her name in game. The catch is that the Japanese lines are normally inaccessible though the game's files, so producing a somewhat accurate translation for them would require me to translate the lines while in game with an auto translator and then write a translation based on what the auto translator produces, but that would have to be repeated for every card on each of the different difficulties, as each variable corresponds to a different difficulty and girl cards can have different effect texts depending on the difficulty. The other approach would be to paste the raw Japanese text into their English card files and translating it from there in the same way that I would translate monster card dialogue, but by doing that I risk the translation failing if my auto translator failed to record even a single character.
An example of the first method would be writing "&フレーバーテキスト, *Insert flavor text here*" into the Japanese Dancer Succubus's card.txt file, which would then produce *Inset flavor text here* as its description in the CG viewer?
Regarding the translation of the event reminisce menu, creating a new directory like you said let me get all the buttons translated real quickly! I would've imagined that translating the close button would require having a line like "&&閉じるボタン,閉じる" in the Japanese StaticStrings.txt and then the line "閉じる,Close" in the English StaticStrings.txt, but I gave it a try and it didn't change anything, so I figure that either the button never references the StaticStrings files, or I got the wrong variable in the Japanese file (both of which are highly likely).
Thank you for bearing with me as I learn all this btw! Your help is very much appreciated and will let me get the translation completed faster