I was born and raised in the US.
I'm have a very high knowledge of English (both technical and casual), took all the honors English/AP courses through college.
I have a somewhat high knowledge of Korean. I can have a casual conversation completely in Korean, but if you want to start talking in "adult conversation" like business, politics, medicine, economics...I just never grew up with that technical vocabulary so it'll be hard for me to follow. (You don't really grow up talking about famine or abortion with your kids. You might talk about "not enough food to eat" but not stuff like "economic depression" -- simple talk vs "technical" talk) My parents moved to the States about a year before I was born. They spoke with me in Korean and I took Korean school on the weekends as a child to learn how to read and write. However my reading and writing is likely around a junior high school level. I did also study Korean in college through the intermediate level (advanced wasn't available), where my final exam included a 5 type-written essay. But I had a few people proof read it for typos >.>
I basically had the same grasp of the English language as I did Korean, the Korean might have even been slightly stronger. I knew the basics of how to read and write both languages by the 2nd grade. I just don't get the practice as much of the Korean.
I studied Spanish in school from junior high until mid-college. During mid-college I'd say I was semi-fluent. I went to Mexico and was able to handle myself around salespeople, having conversations entirely in Spanish. Now though? It's been almost a decade since I studied and although I can get by speaking with my bf's grandmother (she speaks about 5% English and 95% spanish) a lot of the vocabulary is gone from my memory. If I got back to studying it again i'd probably re-learn it somewhat easily, but it'd probably take a good couple month long refresher course of practicing daily.
I've been casually trying to teach myself Japanese but it's hard to try to learn vocabulary without any sort of structure or place to practice it. I've mostly been trying to recognize the hiragana letters for now. Katakana recognition is next, then I figure I'll try to figure out how to pronounce things and try to learn vocab after that. heh. might be backwards. *shrug*