I guess I'll start by saying I was born in the Philippines, but since I moved to California shortly after that (and since my mother has little to no education, so it was impossible for her to teach me Tagalog/Cebuano), I never actually learned my "native" language. The good thing is, I learned English easily, as it was my first language, and grammar and spelling tests were not a problem for me.
However, I strongly believe that after I took Spanish for three years in high school, my English was not in top shape like it used to be. I'm not saying that it takes me a while to say a sentence or anything, but at times, after I say something, I know it sounded weird. Even the sentence before this one sounds like it was worded awkwardly, but I just don't know how else to explain it.
Anyway, more importantly, I never practiced using Spanish enough (besides inside the classroom) to be able to have a normal, basic conversation with any other Spanish speakers. The only thing I truly remember is how to conjugate verbs because my teacher greatly emphasized them. But I suppose it doesn't help that I wasn't really interested in learning Spanish. There were only two languages offered at my high school: Spanish and French, and since Spanish was easier, I took that. To be honest, I also took Spanish because I was aware that some words in Tagalog are the same or similar to words in Spanish, so I figured that if I were to ever become interested in learning my "native" language, that would be a start.
And like practically most of the members on this forum, I took an interest in Japanese after getting into anime, but that's not all. I was always interested in Japan's past history (and ancient Egyptian history), so I'm not just another foreigner trying to learn Japanese so I can brag among other anime fans. Of course, like most people, I tried learning it myself (you know, learning the overused words in anime) and that helped I suppose, but then I really started learning it at Kumon Center for about three years.
Now that I'm in college, I took Japanese both semesters of my first year (which is this year) and I'm doing pretty darn good. Fortunately, even though we learn it at a fast pace (basically three years worth of material in one semester), our teacher promotes a lot of discussion, so we have a lot of practice (which is what I wish my Spanish teachers did). Not to mention, I have a friend who is Japanese (but didn't learn the language until he took it in high school), going to another university, unfortunately, but whenever I talk to him, he demands that I speak in Japanese. At first it's kind of frustrating, but seriously, a lot of practice is what you need to be successful in any language, and I thank him for that.