Chinese Mandarin the official language of China and Taiwan, is widely spoken in mainland China with many different accents due to the vast number of local dialects.
Simplified Chinese is the official title of the written characters used by Mandarin speakers.
Hong Kong, Macau and people from Guangdong region in Southern China will most likely prefer to speak Cantonese and write in Traditional Chinese. If the majority of your visitors come from these regions you should adjust your language availability accordingly.
English is taught in schools from the age of 10 and many young people today will have some level of English understanding and speech. Older visitors are less likely to have a knowledge in English and would benefit from translations into Chinese.
Having a translated website can be a key aspect. It’s better to have no translation than a cheap, bad translation such as with Google translate. Also having a staff member who speaks Mandarin would be a key benefit, but the most costly.