That's what I did. I have spent over 365 days with learning vocabulary. The question is - Am I now able to speak or at least understand my target language? Short Answer: No. If you're interested in the long answer, keep reading!
Why am I learning a new language?
Back then, when this carpool karaoke video BTS Carpool Karaoke by James Corden came out, I was surprised by one member of BTS singing in a really high pitch (see the video at 07:00). I was so impressed by that performance, which led to my beginning of over-investing my time in BTS and their songs. Back then, I didn't know how to match the names of the members to their faces. But with over-investment, everything is possible ;).
Since I've listened to quite a lot of BTS songs, which are sung in Korean, I asked myself if it wouldn't be nice to understand the lyrics of their songs as well. That's how my Korean-journey began.
Why did I focus on learning vocabulary instead of the grammar?
At the beginning, I watched really well made YouTube-videos of people teaching Korean. But I realized it is quite difficult to keep up with the vocabulary and grammar by just watching the videos. After a while, I got time management problems and struggled to spend lots of time in learning. I had to come up with a new idea.
I needed to find a way how to learn consistently with low effort and minimal spent time. Low effort meant deciding on which topic I want to concentrate on: vocabulary or grammar? After a bit of thinking, I came to the realisation: You can know all the grammar there is of a language, but if you don't know the vocabulary, you cannot understand the language solely by listening. But if you know the vocabulary and don't understand the grammar, then you can still understand (e.g. the Korean language) through context. That's why I focus on learning vocabulary and every time I find more time for myself, I would invest additional time in learning grammar as well. But truthfully, this didn't really happen yet.
For learning vocabulary, I got the app Drops. Just like other language apps, it supports multiple languages. I got this app because various resources recommended apps like Duolingo or Babble to learn western languages, but they were supposedly not really beneficial to learn eastern languages like Korean.
Since not all apps on the market provide the option to learn Korean and my goal for now was to only learn vocabulary, Drops was sufficient. Drops is a pure vocabulary learning app. Every word has a recording of a native Korean attached to it, which helps to learn the correct pronunciation. Maybe there are better apps out there especially for learning Korean, but I didn't invest too much time in researching. So, please do your own research as well.
In Drops, you can set up your learning session-lengths as you like when you have a premium account. I set mine for 5 min and used the app now for over a year. Every day in the morning, I started my day by opening the app to have a vocabulary-session. In the beginning, Romanized letters helped me a lot to read the Korean words, but after a few days, I downloaded another app as well, which helped me learn the Korean alphabet. As soon as I got confident enough, I changed the settings to display all words in 한굴 (Hangul / Korean alphabet). Even though it was difficult at the start, with practice, I found myself reading the words quicker and more fluently.
After a few weeks, my motivation sunk, but having to know that you only have to spend 5 minutes a day makes it easy to stay in the habit of learning. The app shows you on what streak you are. (Streak = number of days you have learned through the app without a break.) The first time I tried to keep up my learning-habit, I got to a streak of 100. But then, life happened which led me to missing one day. Knowing that I have to start my streak with zero again made me lose my motivation to use the app. But somehow, Drops got an update and now, you can still keep up your streak, even if you miss one day. The streak finishes if you miss two days in a row. This definitely has changed my life. I passed my 365 days of consequent learning streak. (My current streak is at 431.)
Additional resource: K-Drama
Many other language learners say you learn a language in the most efficient way when you surround yourself with your target language. That's why I started watching K-Drama on Netflix and there are fantastic ones! My recommendation: Itaewon Class.
My experience is: Through constant vocabulary-learning and watching multiple series, you kind of get a hang of most common sentences like 사랑해요 (sarang heyo / = I love you). And with time, you understand more and more, because you start to understand the context. But, I still have to say that if I would have to watch the series without subtitles, I would barely understand anything. There is still room to learn.
Am I now able to understand K-Drama or Kpop through listening? No.
But am I able to understand a few words and sentences? Yes.
According to Drops, I have come in contact with 1602 words till today and most of them are memorised as well. But I find it difficult to build sentences, since I have spent only little time in learning grammar. But being able to understand a few sentences in the series I am watching brings me joy and I believe, if I can keep up the process, my language skills will improve.
I know that if I would spend more time in learning vocabulary and grammar and if I would read texts in Korean, that I would enhance my Korean Level quicker, but as I have also other interests in life, I really enjoy the way how I learn the language right now.
Can I recommend this type of language-learning?
If you want to learn quickly so that you can have real and good conversation with someone in your target language, then I would not recommend this type of learning. At least not only spending 5 minutes a day.
But if you're learning just out of fun without having the necessity to speak in a certain amount of months your target language, then I can recommend this way of learning, since it's low effort and Drops really helps you to keep up with your language-learning-habit.
PS: Here are two Kpop songs of the current most popular boy band: