When Adam Spanberger and his then-girlfriend visited Costa Rica years ago, he sat bemused as she spent an evening chatting in Spanish with her host family from a previous stay. He spoke only English and had seldom ventured farther than two hours from where he grew up in Virginia. She was fluent in multiple languages and loved to travel. “It’s super hot and humid, no air conditioning. I remember sitting on the couch and just listening to her … thinking, this woman is a lot of fun and this is going to be an adventure,” Spanberger said. It was just...