Following are a number of back-translations as well as a sample translation for translators of Isaiah 27:9:

• Kupsabiny: “The Israelites will be completely forgiven
  when (they) have overturned where they worship.
  Their evil/sin shall be washed away
  when the idols of Ashera are no longer present
  and also where they pray/worship with those things that smell sweet (are no longer).” (Source: Kupsabiny Back Translation)
• Newari: “By this Jacob’s sin will be wiped away,
  This will be the result when he removes their sin:
  They will make all the stones of the altar [into] powder like white chalk.
  The pillar of the goddess Asherah and the altar for burning incense will be caused not to stand again.” (Source: Newari Back Translation)
• Hiligaynon: “They can- only -be-forgiven if they will-destroy the rock altars and smash- them -finely, and they will-vanish the posts/[lit. thing-like-pillar] that symbolizes the goddess Ashera, and the altars where they burn incense.” (Source: Hiligaynon Back Translation)
• English: “Yahweh did that in order to punish us for our sins,
  and remove our guilt.
  As a result of our being exiled, all the altars to other gods in Israel will be demolished,
  and we will be forgiven for the sins that we have committed.
  There will be no more poles for worshiping the goddess Asherah, or altars for burning incense to other gods;
  they will all be torn down.” (Source: Translation for Translators)