Mandarin vs. Cantonese (spoken)

Mandarin and Cantonese are the two most well-known spoken dialects among the 7 major dialect groups in China.
Mandarin is the official spoken language of mainland China and Taiwan. It is a standard Chinese dialect based on the northern dialects.

Mandarin is spoken by 70% of the Chinese people in northern and parts of southern China and is understood by 94% of the population. It is the language of instruction in schools and the official language for broadcasting in China. Mandarin is also widely spoken in many countries in Southeast Asia, such as Singapore and Malaysia.

Cantonese is a southern dialect from the Canton area (including Hong Kong and Macau). It is spoken by only 5% of the population in China. Due to historical reasons, most of the early Chinese immigrants in western countries are Cantonese speakers. As a result, it is a prominent dialect amongst Chinese immigrants abroad.

Both dialects are written using simplified or traditional Chinese characters, but the characters which should be used in any translation depend on the place of origin/geographical location of the target reader, i.e. traditional characters for Hong Kong and Macau or for Taiwan, simplified for mainland China.

Simplified vs. Traditional characters (written form)

While Traditional characters are mainly used in Hong Kong, Taiwan and Chinese communities overseas, Simplified characters were specially "invented" for users in mainland China and Simplified Chinese is now the official written language in the People's Republic of China. The idea was to make the language easier to learn and alleviate illiteracy; some Traditional characters had their components either removed or replaced to create a simplified version, while some remained unchanged.