Macbook Air 2017 unable to connect to wifi networks with different country codes
It is simply not true that the MacBook Air is unable to connect to WiFi networks of a different country code. So - no reason can be given.

Your observations have lead you to believe that the above mentioned is true, but something else is really at play. One of the things that "sounds odd" in your description is that you say that "GB" doesn't work, but "NL" works perfectly fine. The definition of what GB and NL allows in terms of WiFi is exactly the same - so there's no difference of having a GB or NL country code when connecting to a WiFi network.

I think you instead have some sort of configuration issue with your Mac. You can try fixing this by opening System Preferences, then click Network and click the "Location" drop-down and choose "Edit Locations". Now add a new location, and setup your WiFi from scratch with that location.

Try using that Location and see if that solves your WiFi issues.