Uniting the world can not be made by language.(and I personally don't believe there will be a world unity in the future) language is part of a multicultural world and a cultural heritage carries the old cultures from past times to present day. A common language makes somethings okay about communication barriers but not at all.Numeric systems and music notes are not a good example because they are different things.We already have English as a universal language but it has not become a world language by purpose of unity.That was a natural result of colonization,wars,trade and it went on by the success of western world at sports,music,broadcasting,aviation and many things.I'd give you an example.After Japan's defeat at ww2,U.S wanted them to change the whole japanese writing system (Kanji) cos that was a big barrier for them to communicate and translate the papers, forced them to do it.But that was senseless.It was impossible to change the thousand years of a tradition so they quit the idea.
Well I don't want a common language in whole world.I want to hear the funny accents of non-english speakers like me,russians,balkans or any other non-english speakers.And also I like scottish and irish accents they sound cool to me as a difference.I'm happy when I hardly understand a latin person but in the end we find a way to deal.One common language means one monotype standardized humans to me.