When I play I usually keep either one of these around: a sheet of paper, a notebook, my phone. Assuming you have a switch you might know the screenshot function! I use it a looooot for japanese learning especially because there is always that day in which you don't feel like stopping to search some words while you are looking forward to playing more.
I do this: set a timer (usually 35 minutes)
30 minutes are for the immersion, taking screenshots if needed or write down if you're more prone to it.
5 minutes are to prepare yourself mentally that I HAVE to stop playing no matter what.
I prefer noting down whole sentences rather than just one word, to remember the way and context where I found it.
After this 35 minutes, if I took a screenshot with the switch I will open the gallery and copy it down on paper and try to translate the things myself intuitively, then I re check it with either chat gpt or a random native person on the internet. If taking a guess is too much I just find the translation!
Then I resume playing, will repeat the process till I get tired or till I actually have time for playing.
But what happens is, in my to do list I mentally write down that those words and sentences I learned will have a digital place (that happens to be my anki deck) By the end of the day I put the sentences and words in my anki.
In games like Pokémon the same words get repeated very often, so I'm sure you'll have no problems remembering vocab!!!
So, assuming you want to play on Gameboy and don't want to stop and note everything down, use your phone to screenshot! And do the same process (if you find it useful of course!! It's your journey!)
Also try to see other people gaming in japanese, doesn't matter whether they're native or not, if it's Pokémon there will be lots of dialogues (yes, also with kanji) You might see the way they reason around a sentence and especially see some kanji as it's a skill you could start early to get used to. Basically for those words you only see hiragana but that more commonly are written in kanji. (Lenghty sentence, sorry ʕ·ᴥ·ʔ)
Now last thing I came to realise when playing in japanese:
Sometimes prepare yourself with vocabulary you already know in your native language before playing the game.
For example: if I'm intending to play Zelda ocarina of time I will brainstorm the first words that I remember seeing as a child in my native language, I search for the translation online (if I don't know that vocab) and then I will start playing and do all of the above. (When you still haven't started a game of course)
If I feel like I really want to live and torture myself, I might also copy down whole dialogues to train my translating skills (sometimes with the intention of translating the whole game, but yeah it's somewhat tiring so to this day I've never finished translating one whole game....the intention... matters..)
other than that, this is basically it. I hope it was useful, and... at the end of the day games are all different and the vocabulary and grammar can be really unusual so don't get discouraged!!! Wish you the best of luck regarding this goal!!!
