Verse 5 contrasts what can be expected from a faithful witness on the one hand, and from a false witness on the other hand.

“A faithful witness does not lie”: “Faithful” in relation to a “witness” means a truthful witness, someone who reports the facts honestly and accurately in court. See 12.17 for “witness”. “Does not lie” may also be expressed positively as “always tells the truth.” See Good News Translation.

“But a false witness breathes out lies”: This is almost identical to 6.19a.

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 .