When you learn another language, you learn another culture. By doing so, you begin to understand that there many different ways of looking at something. This will help you in your career in very, very many ways. Take this simple example: You have hired a freelancer who gives you amazing work, but they have issues with deadlines. Your first thought is to fire them, there are many more freelancers out there. However, if you understand that in their culture deadlines are seen more as suggestions, and time isn't viewed the same way, then you will be more willing to work with them.
It will also help with understanding body language and communication skills. Sometimes we insult people without realizing it because of our cultural differences. When we are familiar with multiple cultures, we are more likely to avoid these accidental miscommunications (even with cultures that we aren't familiar with).