How did spouses talk to each other in international royal marriages in middle age?

For the most part there was a common language between the two parties (usually French). For example Eleanor of Aquitaine was able to communicate with her husband Henry II (who was English) because the English court spoke French at the time. Another example is Marie of Guise marrying into the Scottish royal family. She was French and James V spoke French because most people at his court did. Most royals would have spoken multiple languages. However, there are instances of the two parties not speaking any common language. In this situation the woman would be expected to learn the language of her husband’s home. Until she learned that language they likely would not have spoken much or simply written letters in Latin to one another. Latin was a language that most Catholic royals in Europe could write in. Remember that marriages in the Middle Ages and early modern period were very different from today. It was not about communication and love. It was about duty, commitment and alliances. They often did not need to communicate because they were essentially strangers. Eventually some marriages would become loving but certainly not all of them.