Sorry, Croatian friends, but there is a very clear winner and I'm not sure that you are going to like it. Although the book starts in Syria, and ends in Trieste, most of it is set in a snowdrift outside Vinkovci in which various personal dramas, some based on the then-recent Lindbergh kidnapping, are played out without much reference to the surrounding topography. This book has been invoked explicitly in two different Doctor Who stories. Published in 1934 by the best-known British crime writer of the twentieth century, and famously adapted for the screen in 1974, it is:
Murder on the Orient Express, by Agatha Christie
The book most tagged "Croatia" on LibraryThing, which also does well by ownership on GoodReads, is about an Englishwoman moving to the country and finding herself emotionally engaging with the aftermath of the recent war, by a Scottish writer whose roots are actually in Sierra Leone. Published to wide acclaim in 2013, it is:
The Hired Man, by Aminatta Forna
The most frequently tagged "Croatia" on Goodreads is unfortunately set outside Croatia - it is precisely a story of exile and dislocation, mainly set in Berlin. It is:
Muzej bezuvjetne predaje / The Museum of Unconditional Surrender, by Dubravka Ugrešić
Bubbling under: Slavenka Drakulić, various travleogues