I learned French in school, K-12, immersion. My wife is a native Francophone, and having lived with her and her siblings, it's become second-nature. French has become the primary language in our household (semi-consciously) since we've lived in Anglo communities.
I know a fair bit of Gaelic from my Irish grandparents. But I really only get to speak it is if I'm speaking to my grandfather on the phone, or if I'm visiting Ireland. There are some Irish-speakers in Cape Breton, but it's bastardized, and I fucking hate Cape Breton, have no incentive to even drive through the place, etc. I listen to a fair bit of the music, though.
I learned a fair bit of Latin and Ancient Greek in school, but there's no real need for me to use it ever, unless it really specific situations (Renaissance music, Greek drama, etc.)
I'd like to learn German. I love Berlin.