Slavs
Standardised Slavic languages that have official status in at least one country are: Belarusian, Bosnian, Bulgarian, Croatian, Czech, Macedonian, Montenegrin, Polish, Russian, Serbian, Slovak, Slovene, and Ukrainian.
Origin hypotheses of the Croats
The Slavic, also known as Pan-Slavic and Autochthonous-Slavic theory, dates back to the Croatian Renaissance, when was supported by Vinko Pribojević and Juraj Šižgorić. There's no doubt that Croatian language belongs to the Slavic languages, but they considered that Slavs were autochthonous in Illyricum and their ancestors were old Illyrians. It developed among the Dalmatian humanists, and was also considered by early modern writers, like Matija Petar Katančić, Mavro Orbini and Pavao Ritter Vitezović. This cultural and romanticist idea was especially promoted by the national Illyrian Movement and their leader Ljudevit Gaj in the 19th century.