cities
Chichester
towns
Arundel
Bognor Regis
Burgess Hill
Crawley
East Grinstead
Haywards Heath
Horsham
Littlehampton
Midhurst
Petworth
Selsey
Southwick
Shoreham-by-Sea
Steyning
Worthing
villages
Amberley
Crawley Down
Lancing
Sompting
Wiston
talk
English - dialect is Home Counties.
Speakers of other languages may have trouble being understood, but locals are often willing to be patient and multilingual dictionaries are available at bookstores