@Muddy There is one universal small phrase that almost everyone will recognise
I started school in 1960 and I have always worked and thought in Centigrade or Celsius.
In my senior school, all our science lessons used temperatures in °C and in my further education and in my home heating system and cooking equipment, all temperatures are expressed in °C, so if temperatures are expressed in °F, it means nothing to me - I always have to use “Google” to convert °F to °C to get a feel for how hot or cold it is.
I remember the heatwaves of 1976 - I was married by then and living in County Down in Northern Ireland - I remember the temperatures soaring up to about 30°C that Summer - I have no idea what that equates to under the old system of temperature measurements.
The cookies, biscuits, scones thing is a minefield!
Also jelly/jello and jam/jelly 
I have some family in the States and It can be confusing if you tell them that the temperature was 86 degrees in the summer but gets down to minus 6 degrees in the winter.
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