In a very cold country, if you set an air conditioner to 26 °C, it will likely work as a heater and warm up your room. However, it's important to clarify that not all air conditioners have the capability to provide heating.
Air conditioners that can both cool and heat are called "heat pump" systems. Heat pumps work by using a reverse refrigeration cycle, which allows them to absorb heat from the outside air and transfer it inside to warm up the room. They can also operate in cooling mode during hot weather.
If you have a heat pump air conditioner and you set it to 26 °C, it will switch to heating mode, and the system will work to maintain the room temperature at 26 °C. As the heat pump extracts heat from the outdoor air, it can effectively heat the room even in very cold climates, as long as there is some heat energy available in the surrounding air.
On the other hand, if you have a standard air conditioner that only offers cooling functions, setting it to 26 °C in a very cold country will not heat your room. The air conditioner will continue to operate in cooling mode, but it will not be able to provide the desired heating effect, as it is not designed for this purpose.
In colder climates, dedicated heating systems such as furnaces, boilers, or electric heaters are more common to effectively provide warmth indoors during cold weather. Heat pump air conditioners, with their dual cooling and heating capabilities, are a popular choice for more moderate climates that experience both hot summers and mild winters.