During my visit to Göteborg, I booked a city tour on a tour bus. As I noted earlier, the tour is trilingual. Each point of interest is described by the tour guide three times, first in Swedish, then in English, and then in German. (Even the jokes are the same. You can tell which people on the bus speak which language by checking when they laugh at the jokes.)
I didn't know this when I got on the tour bus. I was simply expecting that the tour would be conducted in Swedish. After all, I'm in Sweden. They speak Swedish here.
The tour started, and the tour guide started by speaking in Swedish, which I sort of understood. Not great, but I got the basic idea.
And then she repeated herself in English. That was a pleasant surprise. Now I could fill in the parts that I missed from the Swedish narration.
Next, she spoke in German, but remember, I didn't know that the tour was trilingual. I just assumed she was returning to Swedish for the next part of the narration, so I thought to myself, "Wow, my Swedish suddenly sucks! I was doing so well and then boom, it's all gone!"
And then I realized, "Oh wait, that's not Swedish. That's German. I can understand this after all."
This is one of those weird language things I've noticed. The languages I learned as a child are kept in one part of my brain, and the languages I acquired as an adult go into another part. When people speak to me in a language I acquired as an adult, I don't even understand them until I first figure out what language they're using. On the other hand, the languages I acquired as a child I can understand immediately. (You can even switch languages in the middle of a sentence and I might not even notice.)