Following are a number of back-translations as well as a sample translation for translators of Isaiah 56:8:

• Kupsabiny: “This is what God is saying
  the one who gathers the people of Israel who were scattered.
  I shall also gather other people
  to add to my people whom I have gathered.’” (Source: Kupsabiny Back Translation)
• Newari: “The LORD Almighty God who free and brings back the exiles of Israel
  declares like this —
  "Besides the ones gathered in one place,
  I will also bring others to assemble with them in one place."” (Source: Newari Back Translation)
• Hiligaynon: “The Lord GOD who gathered the Israelinhon who have-been-taken-captives still said, ‘I will- still -gather the others, not included those whom I have-gathered already.’” (Source: Hiligaynon Back Translation)
• English: “I, Yahweh, the Lord, the one who will bring back the people of Israel who have been forced to go/exiled to other countries, say this:
  ‘I will bring from other countries many more people to join those Israelis whom I have brought back.’ ’” (Source: Translation for Translators)