This could be mechanical things like the order of adjectives, or more complex/personal things on your journey of learning another language.
I want to start learning Norwegian again and I remembered learning a lot about citrus fruits as I went on Wikipedia adjacent trips.
I like the distinction between the two “to be” forms in Spanish (ser/estar) and how it modifies the meaning of the verb. Eg. ser listo != estar listo.
It’s also nice seeing languages with a mostly free word order, that rely on grammar instead, like Greek, even though that probably makes them harder to learn.
This happens in Portuguese too. The first thing we learn in English classes is that the verb “to be” carries two meanings and we should consider the context to identify which one of them is being used.