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.
English to Vietnamese or Vietnamese to English is harder than, say English to Spanish or Arabic because the sounds are so very different - I am sure I simply can’t hear some of the different sounds in tonal languages, and had a friend who moved here from Taiwan when she was so young she learned better in English than Taiwanese but still she could not hear the difference between ear and year.
I don’t think it’s impossible but do think it’s unusual. My dad was bilingual English and Spanish and I wish my parents had done the “one speaks English one speaks Spanish” language immersion but we only spoke English at home.