I’m European, Dutchman specifically, and I find it mentally difficult, almost impossible sometimes, to not converse in English with a person I know does speak English. I used to work at a Dutch company with ~35 nationalities and me and my Dutch colleagues where often reminded by our non Dutch coworkers that they prefer us to continue water cooler conversation in Dutch and not switched to English when they joined in. For them this was a great way to learn more Dutch. Right now there is also a parent at my kids school who is Welsh, and even though he understands Dutch very well and prefers to speak it, everytime I approach him for a conversation the first sentence in my head is formed in English. I have to consciously switch to Dutch before starting the conversation. I don’t know what it is. Maybe it’s some genetic heritage from when our country was a big international trading nation?