Both in the USA and Europe it doesn't matter, it still happens and frankly, I don't know what a 'transition altitude' is. I just fly, or try to, at the altitude the controller tells me.
If the controller tells you something in feet (e.g. 10000 feet), then you need to set your altimeter to the local pressure using the B key.
If the controller tells you a flight level (e.g. Flight Level 100), them you need to set your altimeter to standard pressure (29.92 inHg, or 1013.25 (or just 1013) hPa, depending on what your aircraft needs as input)
The transition altitude is the highest altitude at which the controller will give you an altitide in feet, but you can just listen to the controller.