I think you're taking Matthew 23:9 out of context. Having said that though, I like some of the problem-solving suggestions given. The idea of a global universal language intrigues me. Only, I don't think it should be the primary language but as a mandatory secondary language taught in schools from kindergarten to college.
A people's language is intimately linked to their culture and so I don't like the idea of making people switch to a different language. But I think having one universal secondary language would be a nice way to unite all the various cultures the world over in communication without the need for translators and learning several different foreign lanugages in school. Books, films, songs - you name it - can be published in the international language and marketed to the world market instead of having the additional cost of translating in multiple different languages for different regions. Every educated person would be able to travel anywhere and communicate with the local people in a language they both understand - regardless of the differences in native tongues. The whole world would be able to unite in communication while still preserving the rich diversity of their individual native tongues.
The only problem would be getting all the nations to agree on the specific set of phonetics, vocablary, grammar and alphabet/glyph to comprise the language. I imagine that every different language group will be biased to a system that is easy to them but which other groups might find difficult. What I mean is that because of the great divesity of human language it would be difficult to develop one system that all the nations would find easy and agree to. From a phonetic standpoint I think heavy use of onomatopias can be helpfull. I can easily see all nations agreeing to use the pronounciation "meow" for cat, "ruff" for dog, etc because these sounds are universally associated with these animals. However, difficulty would still come when we arrive at expressing abstract concepts. Maybe we should just all learn to speak Mandarin since that's already the most populous language.