I found FSRS is not great for languages because it optimized for the wrong thing, ie. how likely you will recall a word after X days without encountering that word.
There are 2 big problems:
1. If you are studying seriously, you will encounter many words outside your SRS practice, so the FSRS prediction fails flat.
2. More importantly, language learning is not about recalling words.
The algorithm I use for my app has a different set of objectives, it's <30 lines of straightforward code, and it works better (I tested it for months to be sure about it)
There are 2 big problems:
1. If you are studying seriously, you will encounter many words outside your SRS practice, so the FSRS prediction fails flat.
2. More importantly, language learning is not about recalling words.
The algorithm I use for my app has a different set of objectives, it's <30 lines of straightforward code, and it works better (I tested it for months to be sure about it)
I'll open source it soon