Jakub

With 305 585 bearers, Jakub is the 30th most common masculine given name in Poland (2014 Data). About 100% of bearers of this name are Male in Poland (2014 Data). With 112 095 bearers, Jakub is the 22nd most common given name in the Czech Republic (2014 Data). About 78% of bearers of this name are Male in the Czech Republic (2014 Data).

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Source: https://forebears.io/forenames/jakub

Also Belarusian alongside, Yakub, Jakau, and Yakaw.

Allegedly also Silesian: https://hsb.wiktionary.org/wiki/P%C5%99idawk:Lis%C4%87ina_zapados%C5%82owjanskich_p%C5%99edmjenow

Also Sorbian: https://hsb.wiktionary.org/wiki/Jakub.

Jakub is also a Slovak variant.
Nicknames: Jakoubek, Jashek, Jakes, Kuba, Kouba, Kubes.