Some people have the natural talent to learn a new language. I do not posses such aptitude, but I was fortunate to have other advantages.
My parents' knowledge of French and English really helped their jobs in the old country. Naturally, they wanted their children to learn these two foreign languages early. I started to learn French when I was perhaps 7. There were foreign language schools that offered extracurricular afternoon or evening classes or as summer schools. By the time I was 9 or 10, my parents added English. I thought English was not too difficult to learn after French. Many words were similar, and the verb conjugation was a bit more difficult in French, as it had a few more exceptions. Think of more verbs like "to be" (am/is/are/was/were/has been/will be).
I continued to take these extracurricular language classes until I entered college. However, I stopped taking French classes earlier. I remember the last thing I ever wrote in French, either as a short essay or a dictation, was when I was about 15. That and the fact that I needed to concentrate on English to survive after emigrating to the US were the causes for my French to atrophy. After 40 years of non-use, I can barely read some French, and can no longer write, speak, nor comprehend that well. Still, I retain the love for the French language, particularly the song lyrics I listened to back in those days.
Both of my children have taken French in high school, but they have remembered squat. I do not blame them. It is not easy to retain knowledge of a language if one does not use it daily. I spent many more years learning French, and look at what I still remember. Even with my mother tongue, at this point there are subjects where I would feel much more comfortable writing or discussing in English. I simply may not know or have forgotten the correct words in the native language, although I went to college in my native country. What one does not use, he loses.
There is something very different about one's native language compared to what one learns as a foreign language. Even after all the time living here, I have not been able to appreciate poetry in English, while I still enjoy poems written in the native language. I can still recite some poems from the 18th and 19th centuries that we learned in middle school and high school. My children would never understand them, not even in the literal sense, let alone appreciate the beauty of the word choices in a stanza.
I am still trying to improve my English. To better my writing skills, as I do not have much literary talent including the native language, I have decided to tell jokes or write irreverent posts. Part of humor is universal, but part of it is also language and culture dependent. I know this first hand, as I still remember the first few years after coming here, I did not "get" the jokes I heard or the comedy shows that I watched. If I can get a "real" American to laugh, then hey, I have done OK.