Update, December 16th: Google Play gift cards are now available in all five countries. Good things come to those who wait.
Good news, European readers: physical gift cards for the Google Play Store are coming to more of you soon. Google updated its list of supported countries for gift cards today, marking Belgium, Denmark, Finland, Norway, and Sweden as "coming soon." We can't say exactly when - a few other countries like Greece, Poland, and Portugal got the same treatment earlier this month, and they're still marked as coming soon instead of linking to the relevant page.
Buyers in Belgium and Finland will be able to buy gift cards in 15, 25, and 50 Euro increments, while residents of Denmark, Norway, and Sweden will buy theirs in packs of 150 kr, 250 kr, and 500 kr. The Play Store credit will be good for apps, in-app purchases, and all kinds of digital media, though the availability of movies, books, and music varies from country to country.
At present Google sells or will sell Google Play gift cards in 21 countries. Australia, Hong Kong, and Japan are the only supported areas outside of Europe and North America.
Source: Google Support