more info on that cathedral (thanks to google):http://www.filcoo.com/en/italy/tg/chiesa_di_san_giorgio_dei_greci_venezia_guide.htm
maybe william doesn't speak italian so is looking for something in english.
i suggest going there and even if u don't understand much, stay behind after and ask people (ideally in italian, to be polite) if they speak english and then get chatting. it may be of great spiritual benefit.
i was once in czech republic for 3 days, and i knew only 2 or 3 phrases of czech, but i attended a liturgy in what i think was a mixture of czech and old church slavonic. by the end, i had learnt to say 'Lord have mercy' in russian! i understood v little, but my spirit was lifted up a lot.
after i hung around looking for people to talk to, and heard 2 women talking in a language i spoke, so one of them kindly translated for me when i wanted to exchange a few words with the priest.
eventually the priest remembered some english (it seemed he had learnt it a long time ago) and i found out he had read books by our coptic patriarch, shenouda 3rd! he really liked his books, and it was lovely to hear that in the heart of europe. we had a short, but lovely chat, and i left feeling spiritually full.
i also went to a catholic service while i was there, but on that occasion did not find anyone to talk to because of the language barrier. still, it was nice. so have a nice trip, and let us know how it goes