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.
Horvat
Horvat is the most frequent surname in Croatia and Slovakia, 2nd most frequent in Slovenia and 5th most frequent surname in Hungary. 
The surname originates in Croatia, Horvat being the older version of the word "Hrvat", an autonym used by Croats. In Croatia, majority of Croats with surname Horvat live in the Kajkavian dialect region in Croatia proper. According to the 2011 census, it's the most common last name in the city of Zagreb, Zagreb County Krapina-Zagorje County, Varaždin County, Koprivnica-Križevci County, Bjelovar-Bilogora County, Virovitica-Podravina County and Virovitica-Podravina County. Apart from them, there is a certain number of ethnic Serbs with surname Horvat inside Baranja region of Croatia. Almost half of the citizens of Slovenia that have the surname Horvat live in the Prekmurje region, where it is the most common surname by far. It is also common in Lower Styria and in Ljubljana, while it is very rare in western Slovenia.