But "Et tu brute?" means "You too, Brutus?", but in Latin rather than in Greek, so it sounds like Chinese Whispers anyway.
The point is that Caesar almost certainly didn't say it in Latin.
http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.02.0132%3Alife%3Djul.%3Achapter%3D82
http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.02.0061%3Alife%3Djul.%3Achapter%3D82%3Asection%3D3
Suetonius claims that Caesar didn't say anything as he died, but only groaned a bit. Then he mentions that other Roman authors claim that Caesar said κα? σ? τ?κνον, explicitly in Greek, not Latin, which is completely possible considering that Caesar was fluent in Greek. The first time I'm aware of where someone claims that Caesar's last words were in Latin was in Shakespeare's play. Since then some historians have assumed that Caesar's last words, if he had any at all, were actually Shakespeare's famous 'Et tu Brute?', since at first glance it seems more probable that in his final moments Caesar would speak in his native tongue. But as you can see it does not make any sense to believe so. I see no reason to believe an English poet over a Roman historian, so my guess is that Caesar didn't have any last words at all.