I learned English mostly from playing games as well but that was before I was an adult. I also watched TV in English, read books in English, had English classes at school and had people to ask for help (my parents). I switched my "internal talk" to English. Learning from one source limits your exposure.
I learned Japanese as an adult. I learned some Japanese from very basic study and daily interactions. That gets you to about N5. I needed a rival before I could get motivated enough to hit the books hard. I had a girlfriend tell me about a Korean girl who she was helping read the newspaper in Japanese and she had been in Japan for about 3 years. I had another girlfriend (now my wife) who would study English 7 hours a day. My Japanese was the best among my co workers but then a new guy came, younger than me and above my level (he was studying for N2) Again, I redoubled my efforts. You need a tangible goal. You are probably thinking you want to know Japanese perfectly. You need something you can measure and that is reachable in a reasonable amount of time. Knowing x number of Kanji isnt a good goal, in my opinion, because it doesn't connect to fluency. Think of a kid who says "I can count to 100". That does mean he understands basic arithmetic? No.
As for playing games in Japanese, just start. First few games you play you might not get everything that is going on. Maybe you need an English walkthrough to make sure you got everything important. You'll get better. Sometimes I get tired and stop wanting to look up words I don't know. Sometimes I permit myself to keep playing for a bit more. Sometimes I decide it's time to stop.
Kids are taught to read with the five finger rule.
http://redbridgeserc.org/resources/entry/reading-5-finger-rule/ You can use that to determine if your dialog boxes are too hard. Unforutunately, there are no leveled readers for games but I think some exist for Japanese.
To use a lame analogy, it's like riding a bike. You can read about it all day, look at xtreme bikers but you'll never get there until you get on the bike, hit the curve because you couldn't find the brakes.
Here are some articles I wrote which help beginners.
https://gamekamiwaza.wordpress.com/2014/11/14/new-guide/ basic idea on how to study.
https://gamekamiwaza.wordpress.com/2014/11/14/politeness-in-language/ Why people say anime Japanese isn't real Japanese and similar topics.