The definition of official language from Wikipedia:
An official language is a language that is given a special legal status in a particular country, state, or other jurisdiction. Typically a country's official language refers to the language used within its government – its courts, parliament, administration, etc. – to run its operations and conduct its business.[1] Since "the means of expression of a people cannot be changed by any law",[2] the term "official language" does not typically refer to the language used by a people or country, but by its government