A shared language is a real good — Paul's point that words must be 'easy to be understood' or no one knows what is spoken applies to a self-governing people too: you cannot deliberate together if you cannot understand one another. So the symbolism here is not nothing. The honest part of the ledger is that this changes little in practice — English is already official by statute, and the amendment names no service it would alter — so a voter should not expect it to 'do' much beyond making the statement constitutionally permanent. Critics call it unnecessary or unwelcoming; supporters call it a plain affirmation of a common civic tongue. This is a values vote with low practical stakes: decide whether you want that statement locked into the constitution, and don't oversell either its harm or its effect.
"Except ye utter by the tongue words easy to be understood, how shall it be known what is spoken? for ye shall speak into the air."
— 1 Corinthians 14:9 (KJV)