Christopher Columbus primarily spoke Castilian, which is a dialect of Spanish. Born in Genoa, Italy, in 1451, he grew up speaking Italian. However, during his explorations and interactions with the Spanish monarchy, he became fluent in Castilian as it was the language of the court and the language used by his patrons.
Moreover, as he traveled and interacted with various cultures, Columbus likely picked up some knowledge of other languages, including the indigenous languages of the people he encountered in the New World. However, Spanish remained his primary means of communication throughout his voyages and expeditions.