How did Argentina start speaking spanish?

Answer 1

It was a Spanish colony. This is the same reason that the majority of the countries of Central and South America are Spanish-speaking...and the same reason people in the US speak predominantly English. A colonizing power will force its language on a colonial people.

Answer 2

Argentina's official language is Spanish due to the Spanish colonization during the 16th century. Spanish conquistadors and settlers brought the language to the region, where it gradually became the dominant language through cultural assimilation and intermixing with indigenous languages. Over time, Spanish became firmly entrenched as the national language of Argentina.