In 2010 and beyond there are 2 good reasons for learning a language:
1. Social inclusion
2. Efficient communication
Our world is Web 2.0 enable and it runs at top speed. To keep moving forward and to get the most benefit from global communication we need to smooth the communication paths and we need to ensure everyone can access the Net. Going from one language to another does that. Changing languages as you need to enhances clear and competent communication. Allowing people to express their ideas in their language means you have access to far more ideas and people can express themselves properly.
Second Language Mentor is a very good blog which examines our need to learn languages. It looks at it from a personal and theoretical point of view, so that is a good reading mix. It is a blog which keeps current information about why we need to be learning languages both as individuals and as a global community.