Comments for the name Štefan

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.

Czech name day celebrated on 26th December.

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.