In the past, languages arose because of a lack of communication between different populations. These days every large population can easily communicate with itself, which destroys this avenue for new language creation. However, new dialects of existing languages still arise, and will continue to arise, usually driven by young people seeking to create a distinct culture from their uncool elders. For example, see any Twitch-aware teen and try to decipher half of what they're saying; is "monkaS" in your vocabulary?