I grew up in Romania. Spoke German at home, it was my Muttersprache (German minority in Romania). Went to a German school, but learned Romanian in K-12 there, spoke it fluently. Left Romania when I was 18. I can still understand most when I listen (I can watch Romanian movies not dubbed). I can read it and understand most of what I read. But I cannot form sentences anymore, cannot speak it for the life of me. Pretty strange. I guess it needs effort to revive it in one's brain.