I laughed reading those sentences. (Particularly 上手じゃない hahaha.) I'm honestly confused how you can study actively for a notable amount and forget almost everything. I haven't studied French for over 8 years and I can still read and write almost as much as I remember knowing about it. Sure I remember some more advanced grammatical lessons but have forgotten their rules since then but overall, it's certainly far from lost. As for Japanese, kanji are a curious thing. Besides how amazing they are, the nature of their function and all, I swear some of them are permanently memorized. For example I don't think I can look at 水 and not know that it is water and how to say it as well. I cannot forget it. I have never forgotten it. There are many words I just know.
Of course I haven't abstained from exposure to the language for a long period of time to see what I forget... I don't want to either.
言語を毎日使ったら忘れられないと思う![]()