I'm not an expert in linguistics or any specifics on languages and the depth they may have in different cultures.
However, I do agree that it'd be great to have a language that everyone can understand and use to communicate with each other as it'd have many positives, some which you mentioned above. Having one universal language doesn't necessarily mean the removal of all other languages, but it'd certainly be difficult to have everyone learn one language without forgetting some of another language.
Some languages as I stated above, have cultural significance and many people like to keep their past traditions and cultures alive. All countries / nations / cultures, including isolated tribes if you truly mean everyone, would have to work together to agree on a specific language to use for this and plan accordingly.
Although it'd be a great thing to implement, it probably would be difficult to implement everywhere due to political / economic tensions and whatnot. Still, it's a great idea.