I’ll give a more in depth breakdown soon but for now, I’d probably take a similar approach that I took to learning to read Japanese : learn basic sentence structure, learn top 150ish vocabulary words, avoid books written in non-romaji. Practice hearing spoken word by listening to speeches and following their transcriptions. My exception protocol for unrecognized words was to look them up. And for irregular sentence structure, to guess based on context. It worked for watching movies and reading, mostly but as you can tell, yoi kakikomu koto ga dekimasen*. I’d have to do some thinking on the writing part, it would most likely involve sticking to simple sentences.
*thats terrible Japanese for “I cannot write well”. I think. I hope.
Well of course they do. Because these things are necessary to learning a language. This is the 20% that’s most efficient. By definition someone who puts in 100% of the effort will be doing what I did.
The efficiency of this approach revolves around what you don’t do. You’re excising the 80%. I didn’t spend long hours learning katakana, hiragana and kanji. I didn’t learn the more complex tenses and conjugations. I didn’t spend time on vocabulary words that are highly situational. Contrast this to a typical Japanese textbook.