Mat 12:34 O generation of vipers, how can you, being evil, speak good things? for out of the abundance of the heart the mouth speaks.

This is another verse that gets a little twisted in translation because of how the word poneros, translated here as "evil," comes across in English.

"Generation" is gennêma, which means "that which born or produced." It means "offspring," "fruits of the earth," any "product" or "work." It also means breeding and producing.

"Vipers" is echidna, which means "viper" and is a metaphor for a treacherous wife or friend.

"Generation of vipers" would probably be better translated as "offspring" or "the work" of "vipers" or "the treacherous."

"Evil" is ponêros, which means "oppressed by toils," "worthless," "cowardly," and "useless."

"Good things" is agathos, which means "good," "serviceable," "brave," and "benefit."

The contrast here is between the worthless and the useful, the cowardly and the brave, useless and the beneficial. Agathos has a moral sense of good, but poneros lacks such a meaning except in how it gets translated in the New Testament. Poneros has more the sense of a beaten down, base, cowardly person, not a malicious one.

"Abundance" is perisseuma, which means "superfluidity," "that which remains over," and "abundance." It is from the root, perissos , which means "exceeding some measure or rank."

"Heart" is kardia, which is the physical heart and, in Greek, the seat of feelings, especially feelings that motivate action. Kardia therefore means "inclination," "purpose," and even "mind" as well as "desire."

"Mouth" is stoma, which means "mouth" and "the foremost part" of something. For example, the blade of a weapon is a stoma.

"Speak" is laleô, which means "to talk" and "to speak," but in a light way, as in "to chat," "to prattle," and "to chatter."

A little different but perhaps a closer translation to what Christ was saying:
Ih, the products of treachery, how can you--being useless--say anything productive? For out of the excess of your feelings, your mouth chatters.

Maybe I am defective, but when I study Christ's words, the religious content about the moral good and evil seems much more interesting (and accurately) translated as practical advice about what is useful and what is foolish. To me, Christ is addressing a society of moralizing hypocrites who have lost touch with practical goodness. As I translate his words, they seem most emotional when he goes after people who preach about what is "right" and "wrong" in the sense of "these are the religious rules." His focus is much more on what is "right" and "wrong" in terms of making people's lives better and devel0ping a personal relationship with God.