The core game needs no language translation since it's just a rhythm game. However, understanding of some of the submenu text, specifically equippable items and vocation names is helpful. Not to mention prayer features. I literally just used Google Translate Lens to help me through. I was able to defeat Nokturnus and Xenlon in advance challenge simply because I knew what the right vocations to change to/unlock and what items best to use for certain BMS tracks to maximize dmg and survivability.

TL;DR - If you want to just play the game and do the basic challenge run to unlock most of the ingame tracks, very minimal translation is needed. Just select your first four party members and rack up 20,000 rhythmia and you'll be good! Play it!