My girlfriend has been "learning" a language on Duolingo for about 5-6 years now, but rarely engages with her target language outside of Duolingo and some of her music library. She's been at roughly beginner level the entire time when, with proper language immersion and practice, she should realistically have a large vocab and be able to engage in casual conversation without looking up stuff. This is not the case.

I've just accepted for some time, to her chagrin, that she's effectively playing a game that just so happens to be language themed.