This is the 4350th most frequent Russian word.
болгарского
"Bolgar'skogo" means "Bulgarian" (possessive or related to Bulgaria).
Here, 'болгарского' is used as an adjective modifying 'языка', meaning 'of Bulgarian'.
Я изучаю болгарского языка грамматику.
I am studying the grammar of the Bulgarian language.
In this sentence, 'болгарского' describes 'перца', referring to the type of pepper.
В магазине мы купили болгарского перца.
In the store, we bought some Bulgarian peppers.
Here, 'болгарского' is an adjective describing 'города', indicating the characteristic of being Bulgarian.