Why did J.K.Rowling choose Bulgaria?

Answer 1

Why not?

By the way: there's more than one country mentioned in HP: England, Scotland, Ireland, Albania, Bulgaria, French, Belarus.

If you are asking why Rowling chose Bulgaria as one of the teams in the Quidditch World Cup Final in the fourth book:

She was writing the Goblet of Fire in 1994. In the summer of that year there was a FIFA World Cup held in USA. The surprise of the tournament was Bulgaria. The country had given the world good athletes and individual football players, but had never been known for a strong football team as a whole.

So the thing is that that year Bulgaria's football team finished 4th after losing to Italy in the semi-finals after beating teams like Germany, France, Mexico, Argentina, and etc.

There are suggestions that Rowling got inspired by the great spirit and abilities of such an unknown team.

That is the closest and only time Bulgaria came close to a world title in football.

Answer 2

J.K. Rowling likely chose Bulgaria as the home country of Viktor Krum in the Harry Potter series for its rich history and culture, as well as its association with Quidditch and the Quidditch World Cup in the wizarding world. Bulgaria's reputation as a strong Quidditch-playing nation also made it a fitting choice for Krum to be a talented Seeker.