Ruska Salata is not a traditional Bulgarian dish in fact. As the name would suggest Ruska Salata i.e. Russian Salad. The funny thing it is not even Russian. In Russia, the dish is called Olivie Salad and in fact comes from France. It's called Russian Salad in Bulgaria, because it came to Bulgaria from Russia.
In the same line of thought, Moussaka and Кьопоолу are not originally Bulgarian either. The first one is Greek and the second one Turkish, but they are common, widespread and loved in Bulgaria, so they have become a part of Bulgarian cuisine.