Lua versus Javascript: Why do we need multiple languages?

Wouldn't the world be better if everyone used the same programming language?

This question have been asked many times during the last fifty years, and people continue to ask it. Despite all the apparent advantages (mainly network effects) of a single programming language everywhere, never has a single language dominated the market.

Nowadays, the Internet connects an ever increasing diversity of platforms, uses, and users, each with its onw requirements. The design of a programming language, as that of any other artifact, entails many tradeoffs around conflicting requirements. Different platforms, different uses, and different users need different tradeoffs. As the Internet connects more and more people and things, we will need even more languages, not less.