Telugu is the official language and is spoken by the majority of the populace. However, most educated people will also be able to speak Hindi and English.
Like most South Indians, Telugu people will respond more readily to English than to Hindi. The exception is Hyderabad, where Hindi and Deccani Urdu are more commonly spoken
English is widely spoken in Hyderabad and other major cities. Apart from Telugu, the major languages spoken in Hyderabad are Hindi and Urdu, Tamil in the south and Kannada in the west. Minimum knowledge of Telugu will be extremely useful (but not essential).