Why not? I've learned several languages to varying degrees as an adult, and only had classroom instruction for three of them. I haven't used this method, but I have gotten a great deal out of Chinese video games and I do know a Finnish girl who has learned Japanese to a functional level almost entirely through watching TV. She did some self study on the writing, but nothing beyond what can be (and in fact is!) done in some children's edu games in Japan.
Similarly, I have multiple friends who have learned Cantonese with no classroom time at all.
Well, there's a bunch of mitigating circumstances there. You mentioned classroom instruction for yourself. Many languages are similar so you could have picked up one language quite easily because of its similarity to one you knew already. You mentioned self study. A child (if that's what you mean by "girl") is obviously going to pick up new languages faster than an adult. A children's education game is obviously going to use slower, clearer, simpler language specifically for the purposes of teaching the child. And without more information, for all I know your Cantonese-speaking friends are actually Chinese.
The main reason why I maintain that you do need some classroom time or tutoring or book-learning is that we are adults now.
I think she got into anime in high school. It was definitely well after the critical period for language learning (which btw, many linguists believe is only a critical period for learning a first language).
>for all I know your Cantonese-speaking friends are actually Chinese
None of the Cantonese learners I mentioned were Chinese nationals (though 2 are ethnically Chinese). Even if they were Chinese nationals, it's still far from easy. Cantonese is more different from Mandarin than romance languages are from each other in terms of mutual intelligibility.
My own study history has been French classes with little effect in high school, Japanese classes with much better results in college, Spanish through immersion with mediocre results, many years of living in a bilingual Mandarin environment as well as some classes, and more recently, a bit of Taiwanese, Cantonese and Swedish almost entirely via media until learning enough to try some of it out on people. Taiwanese and Cantonese both have features that are totally alien to me, despite have some distant relationship to Mandarin via classical Chinese. Swedish is totally out there.
I'm 100% sure you can learn languages to a fluent level as an adult through large amounts of exposure to the target language. I've seen it first hand many times and I've essentially abandoned classes for any reason other than visas in foreign countries. That said, reading is great! It's probably the fastest way to build up your vocabulary, even in your native language. After getting enough listening input to have some handle on phonics, I'm all for reading as much as possible. Actually I think not doing that is why my Mandarin progressed fairly slowly until I got into... some video games!
Back to the topic of the article, I would be amongst the first in line to by a Skyrim-style game for learning Swedish or Korean or any other language I want to learn! Anything that's both a source of L2 input and fun is gold.
Similarly, I have multiple friends who have learned Cantonese with no classroom time at all.