This verse is difficult to interpret and does not seem to fit with the verses before it.

“A lying tongue hates its victims”: For “lying tongue” see 6.17. Although the Septuagint and other ancient translations have “hates truth,” Hebrew Old Testament Text Project rates the text of “hates its victims” (literally “hates its crushed ones”) as a “B” and recommends translating “hates those whom she strikes,” or, as in Revised Standard Version, “hates its victims”. In some languages “A lying tongue” cannot serve as the subject of “hate”. In such cases it may be necessary to adjust this line to say, for example, “A person who lies to others hates them and injures them.”

“And a flattering mouth works ruin”: “A flattering mouth” is literally “a smooth mouth” and like “smooth words” in 2.16 refers to deceptive or beguiling talk. “Ruin” renders a word meaning “to cause stumbling.” It is not clear whose ruin is in view, the flattering person’s or his victim’s. Most translations do not indicate who is ruined. Die Bibel im heutigen Deutsch is a typical translation: “Whoever has wounded others with lies must hate them; deceptive talk leads to destruction.” If the ambiguity in the second line must be avoided, we may say, for example, “To hurt somebody by telling lies about them is to hate them and to deceive them is to ruin them.” Contemporary English Version combines the two lines of the verse to say “Watch out for anyone who tells lies and flatters—they are out to get you.”

Quoted with permission from Reyburn, William D. and Fry, Euan McG. A Handbook on Proverbs. (UBS Helps for Translators). New York: UBS, 2000. For this and other handbooks for translators see here .