Andrew Dalby

:* <nowiki>{{CathHierDiocese|scrl|Dioecesis Sancti Caroli Borromeo}}</nowiki>

:gives you

 

:Put that in a footnote. The simplest way to make your pagename is to take off the "Dioecesis" and insert "Urbs". This gives you the name "Urbs Sancti Caroli Borromeo", which is good Latin and is not wrong. You can use it, but also you could then try searching this name and variants in Google Books and see whether you find other examples in Latin texts. You might confirm it, and you also might find other variants of the name that are used more often.