I know a bit more about Liechtenstein than I do about some of these small states, because when I got my first job in Brussels in 1999, Prince Nikolaus of Liechtenstein worked downstairs in the same building; he was then his brother's ambassador to Belgium (whose then king was his wife's uncle) and Luxembourg (ruled by his father-in-law and then his brother-in-law). The Prince and I would often bump into each other in the lobby at the end of the working day, bantering about whose turn it was to lock up for the evening, and he was amused that I was the only person in the building who more or less shared his given name. We stayed in touch after I left that job in 2002, until he left Brussels in 2010.
His country has given me rather slim literary pickings. One of America's best-known romance writers has written a novel whose protagonist is Princess Christianna of Liechtenstein, but as far as I can tell most of the book is set either in California or in Africa. I should point out also that the Princes and Princesses of Liechtenstein are properly referred to as "His/Her Serene Highness", abbreviated to "HSH"; they are not technically royal, so the book has a mistake in its title. (In German one should address them as "Durchlaucht".) The misnamed book, published in 2006, and the 70th published by its author, is:
H.R.H., by Danielle Steel
Having disqualified that on my geographical criteria, I'm going to have to declare a rare tie between two books. Top on LibraryThing, but second on Goodreads, is a short 1955 book by a writer who is well known for his moving, heavily symbolic children's tales (and also one famous disaster story that became a famous movie). This particular book is about a cow whose ardent prayer is that she will be able to produce more milk than the other cows. It is:
Ludmila, by Paul Gallico
The other book, top on Goodreads but second on LibraryThing, is a 2005 non-fiction account of the Liechtenstein national team's campaign to qualify for the 2002 World Cup, in which they lost all 8 matches they played, conceding 23 goals (including 5-0 defeats by Bosnia and Spain). Obviously, half of those matches were played away from Liechtenstein, but from the sound of it there is easily enough of the book set in the country to qualify. It is:
Stamping Grounds: Exploring Liechtenstein and Its World Cup Dream, by Charlie Connelly
Manga fans may also want to note:
The Seventh Seal / 第七の封印, a story line which starts in vol 13 of From Eroica With Love / エロイカより愛をこめて, by Yasuko Aoike.