How is the noble verse: "Allah, He Who made for you the night that you may rest therein and the day enlightening. Verily, Allah is full of bounty to mankind, but most of mankind give no thanks" to be interpreted for the inhabitants of countries that do not experience full day or night?

There are no countries that do not see the sun or where the sun does not set. Rather, the day and night are prolonged in the polar regions. In the North and South Poles, day or night lasts for approximately six months. This does not contradict the fact that night and day are blessings, as the general rule is what matters.