If my hand is laying face up on the table I don't have to say a word as to what my final 5 cards are. All I have to do is show my hand.
Example 1:
Player A is from Russia and Player B is from USA, and they're playing a $1/$2 cash game in Atlantic City. Player A and B are in a pot and it goes to showdown, doesn't matter how. Player B shows his hand, says he has a pair of aces. Player A doesn't speak any english, has no idea what Player B said, so he just shows his hand and has 2 pair, but only speaking Russian doesn't know how to say he has two pair in english. The dealer, will take the two hands, place them next to the community cards, and push up the best 5 card hand. Player A has said nothing to declare what his hand is, yet win the hand because it is the dealers responsibility to make sure the best hand wins the pot.
If a hand is placed face up at showdown, the best hand will win every time and you have to show a better hand than that to win the pot, no matter what you think your final 5 card hand is. I know that when I'm playing live and see two hands get shown I will always say what the best hand is. I have never encountered a problem with this, and have never had anybody argue with my pointing out the winning hand.