Your complaint about scientific names/common names runs rampant throughout the plant and animal kingdoms. Breeders, growers, retailers all tweak names to try to increase sales. Animal names are regulated by the International Commission on Zoological Nomenclature (ICZN). Even these people disagree and change their minds regularly. So why tear your hair out over it?
The scientific name Coturnix coturnix japonica tells its own story: It follows the form Genus species subspecies.
Genus = Coturnix
species = coturnix
subspecies = japonica
Coturnix coturnix japonica is a subspecies of the common quail of Europe and Asia. It is differenciated into its own subspecies because years of domestication and breeding have no doubt brought about differences in egg laying rate, body weight, and temperament. The Coturnix quail raised domestically in Europe, Asia, and America today are the Japanese quail Coturnix coturnix japonica. In turn, the Japanese quail was developed from the common quail Coturnix coturnix.