It's important to note that Quechua is not just one language, but rather a family of languages spoken by millions of people in South America, particularly in the Andes region. The specific variety spoken by the Inca was called Classical Quechua or Runasimi, which was used as a common language throughout the empire for administration, trade, and communication.
While Spanish is now the dominant language in the region, Quechua remains an important language for many communities in Peru, Bolivia, Ecuador, and parts of Chile and Argentina.