History of the Bulgarian language
The history of the Bulgarian language can be divided into three major periods: Old Bulgarian (from the late 9th until the 11th century); Middle Bulgarian (from the 12th century to the 15th century); Modern Bulgarian (since the 16th century). Bulgarian is a written South Slavic language that dates back to the end of the 9th century.
Source: Wikipedia — History of the Bulgarian language (CC BY-SA 4.0)