I didn't understand this phrase, so I asked the developer, MathieuV. I'm posting it here for other translators:
A player "is yielding end game" when he/she negotiates. He/she takes an action that could lead to the game ending. In a sense he/she's open to let the game end; hence this weird formula. There's nothing like this in the rulebook, it's a visual feedback on the rule "when all players negotiate consecutively, the game ends".
It indicates each player whose last action was Negotiate.
It's a tooltip displayed if you hover a player panel/board (which is grey in such cases).