If everyone spoke the same language there would no longer be communication barriers when attempting to open trade with foreign countries. People could more easily form new contracts and there would be no issues with hiring a labor force that can't understand their tasks. While it may be a pipe dream, there is absolutely no question that a common world language would be a recipe for economic benefit.
Should everyone in the world speak the same language: Would the universal language be beneficial economically? Theoretically a universal language could benefit the world economically, but it would be hard to achieve, hard to enforce. [God forbid it would be enforced]. Myth teaches that when the Tower of Babel was being built, the project was possible only because the workers all understood each other. When the height of the tower threatened Heaven, God took away the workers' ability to understand each other, casting them into different languages, ending the project due to lack of communication. Even if the whole world was trained to speak the same language and did not lapse into original languages, eventually regional dialects would emerge from the universal language, perhaps morphing into sub-languages. Because of the distances and differences in cultures I do not think it feasible for a universal language to be established or maintained.
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