Štefan

Also Czech: https://www.behindthename.com/name/s18tefan/top/czech

Štefan is also a Czech given name, used alongside Štěpán in the Czech Republic. The name day for Štefan in the Czech Republic is October 9.

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Sources: https://cs.m.wikipedia.org/wiki/Štefan
https://krestnijmeno.prijmeni.cz/Štefan
https://forebears.io/forenames/štefan
https://en.m.wikipedia.org/wiki/Štefan (shows an instance where Štefan is a Czech surname, derived from the Czech given name Štefan)

Also Czech: https://cs.wikipedia.org/wiki/%C5%A0tefan
https://krestnijmeno.prijmeni.cz/%C5%A0tefan

Although not very common, Štefan is also used in Croatia.
However, owing to the fact that it used to be much more common (second only to Stjepan), "Štef" is today a common short form/nickname for Stjepan.

It´s Slovak, not Slovene.
Slovak pronunciation "SHTE-fahn".

This is a Slovene name, but it is old-fashioned. It was very popular early in the 1900's, but Stefan is the modern spelling.

Edit : both forms are used, Stefan has only recently surpassed this form. Pronounced SHTE-fan in Slovene too, by the way.