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.
Or if your native language is similar to the one you’re trying to learn. If you speak Danish, learning Norwegian is super easy, learning Swedish is easy.
If you’re Italian, speaking Spanish is easy, writing French is easy (even though actually speaking it is harder than Spanish given the strongly different pronunciation).