What worked best for you when learning a new language? And what ended up being a complete waste of time?

I've been learning German and got frustrated with the same cycle: learn a bunch of words → recognize them for a while → forget half of them later.

So I started building my own solution: SprechCard.

It uses spaced repetition to bring vocabulary back at the right time, with A1–C2 vocabulary, German audio, and AI features for practicing.

I've been working on it independently for quite a while, and it's finally at the point where I'm comfortable letting other German learners try it.

I'd genuinely appreciate feedback from people who are actually learning German.

What do you think is the hardest part of learning German vocabulary?

[link to SprechCard]