Following are a number of back-translations as well as a sample translation for translators of Proverbs 26:9:

• Kupsabiny: “When/If a foolish person uses a proverb
  it is like when a drunk person is holding a thorn(bush).” (Source: Kupsabiny Back Translation)
• Newari: “For a fool to recite a proverb
  is like a drunk trying to remove
  a thorn from his hand.” (Source: Newari Back Translation)
• Hiligaynon: “The proverb that the foolish-ones is-saying can-harm like a thorny bushes which a drunkard is-holding.” (Source: Hiligaynon Back Translation)
• Kankanaey: “The advice of a foolish-person is like thorns that a drunk-person waves-back-and-forth.” (Source: Kankanaey Back Translation)
• English: “If a drunk person waves some thorns/brambles with his hand,
  he is not able to accomplish anything useful by doing that (OR, he does not feel it when a thorn sticks in his hand);
  similarly, if foolish people speak proverbs,
  they do not help anyone who hears them.” (Source: Translation for Translators)