Netherese are an ethnic group of humans residing in Netheril. Many cultures are either descendant or have been absorbed as Netherese, such as the Shadovar, the Halruaans, the Bedine, and the Illuskans, etc.
The Netherese have always lived in a magical society. Currently the netherese are rebuilding their mythallars so that they can once again live above "those who fear and don't understand magic". They use the orcs as slaves for two reasons: to finish the extermination of the orcs by "domesticating" them, and to rebuild their empire to heights never before seen.
The common Netherese speak Netherese while the nobles speak Loross. The reason for two languages is for separation of the classes.