A person's language comes majorly from his/her history, beliefs, values, background and environment. For example, if a person is born in America, the culture, background, beliefs he/she is exposed to is of America, so the human mind adopts the same and then the english language is also adopted by the person as that is prevalent in the background of the country.
The basis of any person's language is the culture, belief and background he/she comes from. For example, in India, there are multiple cultures, beliefs and chunk of people have different backgrounds and history. On the basis of these there are different languages in the country. People have different slangs and different way of saying the same thing in their own language. The culture, belief, background, values and the environment around a person makes the language of a person.