In Genesis 11:6, as man is building the Tower of Babel, God says that,"If as one people speaking the same language they have begun to do this, then nothing they plan to do will be impossible for them." Does this mean that man is literally omnipotent if we are united behind one language? How can this be reconciled with God's omnipotence?
They will not be omnipotent; they'll only be able to do what they plan to do. Our plans are limited by our thoughts; thoughts expressed in, amongst others, language. We're mere humans, created as images of God (Genesis 1:26), so we can never fully fathom what is possible to God (see also Luke 18:27). So even though mankind might have deemed themselves omnipotent if the Babel collapse didn't happen, they simply lack the imagination of what it means to be fully omnipotent.