Esperanto.
Esperanto is a language created by Ludwik Lejzer Zamenhof which tried to be the second language for different countries in order to uniform them. Initially, its name was "Lingvo Internacia", which litterally means "International Language", indeed explaining what it was made for.
Having an international language, either as a first language spoke by anyone and anywhere or as a second language teached with fluency in mind since kindergarten, would make translators not needed anymore for translations for political transactions and international congresses and the likes. I've got no data for that, but I remember hearing it somewhere in TV, and for sure it was in the order of billions of Euros only for the EU.
Other than that, travelling would be much easier, and the integration of immigrants in the new country would be much easier.
While I'm not talking specifically of Esperanto, would having an international language be possible in a future? Would you like it? Do you think it will ever be done?
[I put this in politics because, IMHO, this is where it belongs. If a mod finds it to be the inappropriate board, feel free to move it]