What I'd like to have is an app that allows me to easily select specific vocab that I want to learn (with flashcards).

Essentially, I would pick "cooking" and get a list of vocabulary, sorted by usage/importance that contains all the words that I need for "cooking" such as tools, ingredients, techniques and so on.

Or the same for traveling, hiking, cycling, ordering in a restaurant, buying a house, ...

That would be super useful.