Our company (Language Zen) has this patent https://patents.google.com/patent/EP1891619A2/en
and we have done work to teach hierarchical knowledge for language learning
I say this as someone who was deeply involved in the industry in the late 2000s. I also contributed to Anki in that time frame.
For example Skinner's Learning Machine as well as any automatic implementation of Pimsleur's method, both described in the SIXTIES, would fall under this (according to my reading, I'm not a patent lawyer, hamdulillah).
Absurd.