Herrscher der Welt

Slavic "mir" meant not 'Welt (world)' but 'peace'. Modern Russian "mir"=world is late neologism! Proto-Slavic name was Voldimirü (where ü=hard jer, supershort vowel, similar to u/y) from Voldi-ti (to rule) and mirü (peace). Names with root Voldi- were very popular in Slavic languages. The word voldi-ti 'to rule' is still used in modern Slavic languages.