I've been spending hours researching different medieval kings and emperors and their families. When you do that you start notice how often they married princesses and other noblewomen from other kingdoms and realms. I get why this was done but what has always bothered me is how exactly did they communicate with each other?

Holy roman emperor Henry IV had an ukrainian wife. His father Henry III had a Danish wife. Otto II was supposed to marry Zoë Porphyrogenita, a Byzantine princess. Several emperors of HRE married english princesses. Richard Lionheart and many other English kings had castilian and navarrese wives. The list goes on.

How did they understand each other? Did they need translators when they spoke to each other? Would the woman have to learn the language of her home? Was there some kind of common language that they would know, like latin or something?