Many of the best Bulgarian novels often deal with the country's history. For example, they might depict the struggles for independence or the effects of different political regimes on the people.
Love and cultural identity are likely main themes. The story probably explores how love is shaped by Bulgarian culture, traditions, and the unique social environment of Bulgaria.
There's no official indication in the original 'Harry Potter' series that Harry knows Bulgarian fanfiction. Fanfiction is a creation of the fans outside of the official canon, and while Harry is a wizard well - versed in many magical things, Bulgarian fanfiction isn't likely to be on his radar in the context of J.K. Rowling's books.
If Harry Potter knew Bulgarian fanfiction, it could be really interesting. Maybe he would be amused to see how fans from Bulgaria have imagined different scenarios for him and his friends. He might learn some new perspectives on his own adventures that he hadn't thought of before.
Love is a key element. The adoptive families that truly love the Bulgarian children they adopt are more likely to have a success story. For example, families that show unconditional love help the children feel secure.
One possible plotline could be that Hermione is chosen to be an ambassador of sorts for the Hogwarts students when they visit Bulgaria for a magical exchange program. So, she has to learn Bulgarian quickly to communicate effectively, and this leads to various adventures and cultural exchanges.
A third famous Bulgarian novel could be 'Fever' by Georgi Gospodinov. It is a thought - provoking work that often plays with different narrative forms and themes. It reflects on various aspects of modern Bulgarian life, including identity, relationships, and the general state of the society in a rather unique and engaging way.