Quechua was a language spoken throughout which empire?

Quechua also known as runa simi ("people's language"), is an indigenous language family spoken by the Quechua people primarily in the Andes of South America. Derived from a common ancestral language, it is the most widely spoken language family of indigenous peoples of the Americas, with a total of probably some 8–10 million speakers. It is perhaps most widely known for being the main language of the Inca Empire.

The term Inka means "ruler" or "lord" in Quechua and was used to refer to the ruling class or the ruling family. The Spanish adopted the term (transliterated as Inca in Spanish) as an ethnic term referring to all subjects of the empire rather than simply the ruling class. As such the name Imperio inca ("Inca Empire") referred to the nation that they encountered and subsequently conquered.