This might not work, but the phonetic way of writing the pronunciation is:
siwtəðˈeʎə
There are plenty of Spanish speakers here on GN so I hope I'm not treading on anyone's toes telling you that the Spanish pronunciation would be Thee-oo-ta- della.
Menorca uses Catalan and its own patois, which is a version of Catalan - the road signs are in three languages.
I was on Menorca about 20 years ago but can't remember if we went to Ciutadella or not. It's a good idea to find out as much as you can about the place before going though, you get far more out of the holiday that way!