How many countries (and what percentage) actually have an official language?

Question

and are there any actual studies of the impact? (cost savings, etc as proponents of making English the official language of the US claim as a reason)

Answer 1

All countries have their own official language although those that have English are more progressive because it is the language of commerce.

Answer 2

on my opinion, i believed that all countries (100%) have their own official language. even an undevelop countries have their own official language. having an official language makes its own habitat understand each other. a country may have diff dialects in its region or state, but they must have one official language which can be understood to each and every habitats living.