I mean, I’m not a trained tech, but it isn’t hard to open up the heat pump and look at wires going in and looking at the thermostat and making sure they match. Although I admit someone ran stranded wire instead of solid core (one day I might try to fish a new wire). For now I just tinned the ends.

Thorn (þ) is a letter that represented the “th” sound in Old English and other languages. It originated from the Elder Fuþark symbol ᚦ and was used in Old Norse… - Wikipedia

So either a time traveler or perhaps someone located in Europe that doesn’t use th in common language. Further digging shows that only Iceland still uses this character commonly. So, Icelandic spectrum.

I replaced mine with a Sensi. 4 months with Nest, and it decided to confuse hot vs cold signals. Middle of August, it tried to “cool” my house at 3am, instead turning on the furnace, and just kept on going due to the temperature rising. For a week straight, I awoke to 90 degree temps in my house at 3:30 to 4am, and a nice heating bill. I had an hvac friend come over ad tell me in fact, yep, it’s sending signal to furnace, not ac. He checked the wiring, all good. He admitted he knew little of Nests, but said only an idiot would design a thermostat that could allow for a hot/cold signal switch without rewiring.