We've already got it: English. Just as Latin was the pan-European language of diplomacy,law, science, learning and commerce hundreds of years ago , and French became so to a degree, so English is now.In those days educated people had to learn those languages in order to communicate their ideas universally, now they have English instead and this requirement extends farther in the world than ever before.
In France,for example, we find major French companies publish their results and directors' reports in English. Even internal memos and rules for managers are in English (giving rise to complaints that safety might be compromised in some cases) and published in French, if at all, later.We have had examples of meetings conducted entirely in English when, unbeknown to the participants, everyone present was in fact francophone ! The march of English is unstoppable.
The only problem may be that , at a local level, varieties of English may flourish.Then , as once in England itself ,speakers of the language may find difficulty in comprehending other anglophones because of differences in dialect.