I think it is absolutely necessary to learn your significant others language. It's hard enough communicating as it is. When you cannot communicate efficiently with your significant other, it's very hard to understand where they stand in life. It would be difficult to understand their dreams and aspirations. I would hate to not be able to communicate with the person I love, regardless of how much physical contact there was. What happens when you become lonely and need someone to talk to? What happens if you are having a medical issue that needs to be addressed? It's so important to be able to communicate.