If you buy an Apple Watch abroad, these devices are supposed to be used in the country of purchase, due to the different built in hardware, that has to support local carriers, especially if it comes to LTE.
So make sure that your carrier in Poland supports this model and all its features.
And the watchOS is also country specific. An Apple Watch bought in the China will always install the Chinese watchOS version and all available features and restrictions for the China. Features that are specific to the Polish/European watchOS will not be supported in that case.
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To cover the LTE and UMTS bands used around the world, there are two separate cellular models for Apple Watch. They have been optimized for use in the country of purchase, and not all models work in all countries or regions. There is no single model that supports cellular service worldwide. To see which carriers in your country or region offer cellular service for Apple Watch, refer to the chart below.
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copied from: Apple Watch - Carriers - Apple
Also remember, that the warranty for an Apple Watch can be restricted by Apple to the country of purchase.
In case of a warranty claim, you will have to bring the watch back to the country of purchase, Apple Support does not ship internationally.
Apple One (1) Year Limited Warranty