This will be a world as it was before the Tower of Babel, when all spoke one language. In the future, when all has been repaired, all will return to how it was; a shared vocabulary, a universal language, one based on seeing God in every detail of creation (Yismach Moshe).
However, although all will speak this universal language of praising God, many will be speaking but not reflecting their inner hearts. The promise, as described in our prayer, is that we will merit that we, our children, and all our future generations will speak a language that reflects the purity of the inner soul (Reb Tzadok haKohen of Lublin; Resisei Layla, page 36).