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On Earth, our temperature scales are calibrated based on some universal (on Earth) values. For example, 212°F and 100°C are defined as the temperature water boils at sea level.
How are these calibration values decided on other planets? Many planets don't have a 'sea level' and if they did, atmospheric pressure would still be different. How would thermometers be calibrated on other planets?
I think you have it backwards - it doesn't matter where in the universe you are, absolute zero is still the same (-273.15°C) and the temperature increase marked by 1 Kelvin or 1 Centigrade is the same, so you could find a calibration point on any planet that came to the same temperature and list that as the way to measure 100°C etc.
Realistically though, you wouldn't need to do this, and you just wouldn't use a thermometer that had any gaseous or liquid connection to the outside environment. It is much easier to not have to worry about it.
Calibrate your thermometers on earth before you go traipsing round other planets.
