Initially, and for many years, we also tried to not have a subscription but steady development needs to paid somehow, same goes for customer support. If Apple would allow for paid upgrades…
A lot of people seem to like shared card decks but creating your own cards is part of the learning process, you spent time with the material you want to learn, which is the main thing that helps you learning.
shameless self-plug:
On macos and iOS we found Anki a bit out of place so we build a competitor explicitly for language learning (https://wokabulary.com/).
Looks like a fun project and Java really could need a bit of minimalism. I'm always intrigued by small frameworks like Minum et al. even if it's just to learn how things are done in an approachable way.
Love to see stuff like this on HN, and I'm a bit surprised about the negativity in the comments.
For a real world project pick a suitable language that will not only help you to implement whatever you have to implement but also to maintain the project. Also you should be able to find other programmers knowing that language if you need to. Maybe even use the language you already know even if it is not the newest and hottest stuff.
But for private or side projects use whatever enlightens you. Those projects should be fun and it's always good to learn new things on the way. I even think you don't have to learn all new languages in depth but just do a small project and reflect if it is something that gets you somewhere. You probably wont write a big business application in Smalltalk but all that message passing, awesome. Seriously have a look at Smalltalk.