Following are a number of back-translations as well as a sample translation for translators of Jeremiah 9:5:

• Kupsabiny: “A person cheats/deceives his friend
  not even one (person) still speaks the truth.
  (They) have taught their tongues to lie,
  and their sin/rebellion has enveloped/engulfed those people.” (Source: Kupsabiny Back Translation)
• Hiligaynon: “Each one deceives his fellowman, and no one is telling the truth. Their tongues were used to lie, and they wear-out themselves to sin.” (Source: Hiligaynon Back Translation)
• English: “They deceive their friends
  and never tell the truth.
  They lie continually and, because of that, they have become skilled liars;
  they do one oppressive thing after another, and are unable to stop doing it.” (Source: Translation for Translators)