Polish zloty (PLN) currency no longer appears on the list of currencies, neither in the website's footer, nor in the Settings section. I have tried switching languages multiple times. Can someone confirm? Is this an intentional change or a glitch?

UPDATE: Clearing browser cache and gog.com cookies fixed it for me.

It's there for me, I can see PLN.

Add anything to the cart and proceed to checkout. It should fix itself.

Clearing browser cache and gog.com cookies fixed it for me.

Well in essence, among containing useless marketing data, the cookies typically contain settings which if you don't know how to fix, are best fixed by taking a phaser and vaporizing the damned thing.

There's generally only one cookie which needs to be deleted, gog_lc - that stores the country which gog detected you to be in, as well as the chosen currency from among the provided choices for that country. Without the cookie, gog will run the detection again (as it also does on the checkout page), with a high probability of getting it right the second time.