Tarski's hidden theory of meaning: Sentences say exactly one thing

I argue that Tarski's truth schema (T) concerns meaning just as much as it concerns truth. Better said, (T) implicitly presupposes a theory of meaning; it rests on a simple and yet contentious assumption, namely what Andjelković and Williamson [1] have termed the principle of uniformity (U): every sentence of a language says exactly one thing. I here challenge the validity of (U), and, insofar as (U) is a necessary condition for the validity of (T), I conclude that (T) is false