I made a simple flashcard system for avatar3.0, using the random parameter driver. example avatar in webm related plus the hiragana flashcards:

https://files.catbox.moe/qaslek.unitypackage

I don't now a good way to make the animators and stuff generic, so if you want it on a different avatar you'll probably have to stare at the setup long enough to understand how to copy it. The flashcards themselves are just packed into a texture and the shader switches between them on an animatable parameter. I used imagemagick to generate and stick all the text into a grid. It's theoretically possible to generate images from e.g. anki decks, but would require additional autism to parse the xml and stuff. Also, this is just random choice, not spaced repetition. You could in theory stick enough state into an animator state machine to implement spaced repetition but that'd be some very serious autism.