> without calculation, I can’t express the temperature outside in Celsius

I think you'd get used to it rather quickly if it becomes ubiquitous in your daily life. It's probably a little bit similar to when there's a change in currency or some such - like when the EU introduced the Euro. Someone here could maybe confirm from personal experience but my German and other EU friends all mentioned that in the first few weeks it was quite the headache, "is this price expensive or not", but after a while the numbers start to stick and make sense of their own.