I’m from Vietnam. I’ve been in the UK for 10 years now. When I met my English husband 13 years ago at 19 I knew 0 English. We communicated using machine translation. So that’s when I started learning English. Fast forward to present day after immersion, living in an English speaking country, formal study, etc. and I’d say my writing and listening (understanding) are good, but my speaking and reading are still bad. I kind of gave up on trying to become fluent at this point.
I’m fluent in English and Spanish, et je suis en train d’apprendre le français
Though I will note that of course, learning a language that’s in the same “family” of languages as your mother tongue will always be easier, regardless of age. The jump to Japanese or Arabic from English is far greater.
Dutch is my native language so not sure how close that is to Japanese, ha. But I understand what you mean.