The essay focuses on the role of the Italian language under the episcopate of Arnošt Vojtěch of Harrach. After analysing the increased use of the Italian language in Vienna and Central Europe in the Modern Period, the author turns his attention to an exceptional case in Cardinal Harrach’s circles, which often employed the Italians in connection with a fundamental reform of the Czech religious life. In the second part, the author concentrates on political activities of the Capuchin Basilius von Aire (1591-1665), who communicated with Harrach only in Italian, although he was not an Italian. After departure of the famous Capuchin Valerian Magni, this man became a chief advisor to the cardinal; their communication thus constantly involved the most acute issues of the mentioned reform. Although Basilius von Aire represents one of the most important persons of the Prague society in the 17th century (even with regard to Harrach’s attitude to the Jesuits), he had remained an almost unknown figure until recently.