Well... I speak Danish fluently, so it would be weird if I spoke English in Denmark.
And of course, when I'm in an English-speaking country, I speak English.
I learned German in school, so I speak German, when I'm in Germany.
I'm not fluent in it, but I still feel like if I don't use German, then all the stuff I learned in school would be for nothing.
There are times when I learn a bit of a language before I go travelling to a country. (basic stuff like "sorry", "thank you", "hello" etc...)
Even though I might not actually end up using any of those words.
And many countries have people who speak English.
I remember when I was trying to teach myself French because we were going to travel to Canada.
But I was in the English-speaking part of Canada, so I didn't even need French...