I can comfortably understand what I've been into (enough to enjoy it despite the ambiguity). I'm not a beginner, I'm at intermediate level and I would say I have about ~4k vocab.

Is there a guide to quickly (or as efficiently as possible) becoming able to translate well? And I mean via self-study, not with university or tutors. Or like, what would the roadmap or learning route for that look like?

Because the way I've been learning for my own casual interests so far has been like this:

Get into media (any game or manga or anime etc) that isn't too hard for me. Look up unknown words if I feel I've seen them before. Perhaps do more look ups in the beginning. After a few days of light immersion (30-60 mins) I become used to the media and I've picked up most of the commonly used domain-specific vocabulary and I just breeze through the rest of it. I don't do any "formal studying" other than occasionally looking up grammar I find weird and conversing with natives and having them correct my Japanese.

However I don't usually have precise 100 percent understanding, even though I can follow along the story fine. I wonder how I would have to alter the way I learn Japanese to become a translator?

[I want to translate manga and novels, and things like that]