Chakavian
Chakavian in its actual use is the least spoken Serbo-Croatian dialect, being spoken only by 12% Croats. It is now mostly reduced in southwestern Croatia along the eastern Adriatic: Adriatic islands, and sporadically in the mainland coast, with rare inland enclaves up to central Croatia, and minor enclaves in Austria and Montenegro. All areas of old contacts with Romance languages.
Serbo-Croatian
Enisa Kafadar argues that there is only one Serbo-Croatian language with several varieties. This has made it possible to include all four varieties in a new grammar book. Daniel Bunčić concludes that it is a pluricentric language, with four standard variants spoken in Serbia, Croatia, Montenegro and Bosnia and Herzegovina. The mutual intelligibility between their speakers "exceeds that between the standard variants of English, French, German, or Spanish". Other linguists have argued that the differences between the variants of Serbo-Croatian are less significant than those between the variants of English, German, Dutch, and Hindi–Urdu.