Chinese and English are the official languages of Hong Kong. Although the majority people in Hong Kong speak Cantonese which is a dialect of Chinese. Mandarin Chinese is also widely used in Hong Kong.
Most people in Hong Kong have studied English in school and therefore using English during your trip in Hong Kong should have no problem for communication.
However It is recommend to install translation app such as Google Translate in your smart phone in case you needs support on communicate with the local people.
Here is a list of useful Cantonese Phases for your travel reference:
|Hello How are you?||你好嗎?|
|Thank you (if someone give you a physical item)||謝謝|
|Thank you (if someone does you a favor)||唔該|
|Could you take me to ……. (when you tell the taxi driver)||你能帶我去…..?|
|Can I have ……… (when you place an order||我想要……|