Following are a number of back-translations as well as a sample translation for translators of Proverbs 12:23:

• Kupsabiny: “A wise person does not show how big his knowledge is,
  but the fool tells out/exposes his foolishness.” (Source: Kupsabiny Back Translation)
• Newari: “Wise people do not show off
  their skill and learning.
  But fools display their foolishness.” (Source: Newari Back Translation)
• Hiligaynon: “A wise man does not boast what he knows, but a fool man he surely shows his foolishness.” (Source: Hiligaynon Back Translation)
• Kankanaey: “The careful/circumspect, he does not relate what he knows, but the foolish-one, he talk-loudly-about what is useless.” (Source: Kankanaey Back Translation)
• Shilluk: “A person whose head is present (i.e., a wise person) speaks thoughtfully,
  but the person whose head is small (i.e., a fool) just gurgles.” (“Here the wise person speaks thoughtfully or deliberately. In contrast, the person who is a fool is vividly described using a powerful metaphor-in the same way that a pot of porridge boils over into the fire, so a foolish person’s words gurgle out of his mouth. His speech is neither deliberate nor controlled.” — Source: Cynthia Miller in The Bible Translator 2005, p. 129ff. )
• English: “Those with good sense do not reveal all that they know;
  foolish people show clearly by what they say that they are ignorant/have not learned much.” (Source: Translation for Translators)