If a universal language exists, then for every two people if they both know the same universal language they can communicate.
∀x ∀y (∃z (¬(x=y) ∧ Know(x, z) ∧ Know(y, z) ∧ UniversalLanguage(z)) → CanCommunicateWith(x, y) ∧ CanCommunicateWith(y, x))