From Is That a Fish in Your Ear?: Translation and the Meaning of Everything by David Bellos:
"In the late Middle Ages, the situation was quite similar in many parts of Europe. Traders and poets, sailors and adventurers moved overland and around the inland seas picking up and often mixing more or less distantly relate languages as they went, and only the most thoughtful of them every wondered whether they were speaking different 'languages' ore just adapting to local peculiarities. The great explorer Christopher Columbus provides an unusually well-documented case of the intercomprehensibility and interchangeability of European tongues in the late Middle Ages. He wrote notes in the margins of his copy of Pliny in what we now recognize as an early form of Italian, but he used typically Portuguese place-names--such as Cuba--to label his discoveries in the New World. He wrote his official correspondence in Castilian Spanish but used Latin for the precious journal he kept of his voyages. He made a 'secret' copy of the journal in Greek, however, and he also must have known enough Hebrew to use the astronomical tables of Abraham Zacuto, which allowed him to predict a lunar eclipse and impress the indigenous people he encountered in the Caribbean. He must have been familiar with lingua franca--a contact language made of simplified Arabic syntax and a vocabulary taken mostly from Italian and Spanish, used by Mediterranean sailors and traders from the Middle Ages to the dawn of the nineteenth century--because he borrowed a few characteristic words from it when writing in Castilian and Italian."
Bolding is my own. Reading on Kindle, so I don't know the exact page number, but you can find that excerpt at location 137-150.