Therefore thus says the Lord GOD. This new mention of the speaker helps in Hebrew because there is a change from talking about the people of Israel (verse 10) to talking to them (verse 11). Such a change, common in Hebrew, is frequently confusing and awkward in other languages. The Good News Translation has therefore restructured verse 11 so as to have the Lord still talking about the people of Israel, and so the speaker does not need to be mentioned again.
An adversary shall surround the land/And so an enemy will surround their land. This is the best way of understanding the Hebrew, although there are problems.
And bring down your defenses (Hebrew: strength) from you/destroy their defenses. One possible translation is: “and strip you of your strength” (New American Bible), or if the translation has God speaking about the people of Israel: “and strip them of their strength” or “make them weak.” On the other hand, the Hebrew word for “strength” may mean “fortifications,” “defenses.” So Good News Translation has destroy their defenses. Since many languages do not have a general word for defenses or for certain types of fortifications, the nearest equivalent expression may be “destroy the places where they hide/protect themselves.”
Quoted with permission from de Waard, Jan & Smalley, William A. A Handbook on Amos. (UBS Helps for Translators). New York: UBS, 1979. For this and other handbooks for translators see here .
