Proverbs 12:23 New English Translation

²³The shrewd person^[a] conceals^[b] knowledge,
but foolish people^[c] proclaim folly.^[d]

Proverbs 12:23 tn Heb “a shrewd man” (so NAB); KJV, NIV “a prudent man”; NRSV “One who is clever.” sn A shrewd person knows how to use knowledge wisely, and restrains himself from revealing all he knows.
Proverbs 12:23 sn The term כֹּסֶה (koseh, “covers; hides”) does not mean that he never shares his knowledge, but discerns when it is and is not appropriate to speak, cf. 10:14; 17:27.
Proverbs 12:23 tn Heb “the mind of fools.” The לֵב (lev, “mind, heart”) is the place of thinking and so it is the both source of what is said and the place of discernment for what to say aloud.
Proverbs 12:23 tn Or “speak out foolishly.” The noun may be a direct object (folly) or an adverbial accusative (foolishly).sn The noun אִוֶּלֶת (ʾivvelet, “foolishness; folly”) is the antithesis of perception and understanding. It is related to the noun אֱוִּיל (ʾevvil, “fool”), one who is morally bad because he despises wisdom and discipline, mocks at guilt, is licentious and quarrelsome, and is almost impossible to rebuke. W. McKane says that the more one speaks, the less he is able to speak effectively (Proverbs [OTL], 422). Cf. TEV “stupid people advertise their ignorance;” NLT “fools broadcast their folly.”

New English Translation (NET)