Learn Farsi: اقتصاد جهان در آستانه‌ی فروپاشی است، مگر نه؟ - The world economy is on the threshold of collapse, isn't it?

Dar âstâne-ye translates to "on the threshold of" or "on the verge of". It requires an Ezafe to connect it to the noun or infinitive that follows—in this case, the noun foroupâshi (collapse). Because the word âstâne ends in a silent 'h' (ه), the Ezafe takes the written form of a 'ye' (ی) to link the words.

Could I use the other phrase from this lesson, dar shorof-e, in this sentence?

Yes, you could completely substitute it to say dar shorof-e foroupâshi است. Both phrases show imminence. However, dar âstâne-ye (which literally means "on the threshold") is especially fitting for major, dramatic shifts like an economic collapse, while dar shorof-e is often a bit more general, like saying something is simply "about to" happen.

How is the noun foroupâshi (collapse) formed from its verb?

It is derived from the compound verb forou pâshidan (to collapse or disintegrate). Farsi frequently creates abstract nouns by adding the suffix -i to the present stem of a verb. The present stem of the verb here is pâsh, so combining the prefix forou, the stem pâsh, and the suffix -i creates the noun foroupâshi.

Why does the tag question just use magar na for "isn't it?"?

English tag questions are notoriously complex, changing based on the subject and the tense of the sentence (e.g., "isn't it?", "don't they?", "haven't we?"). Farsi is much easier: you can append (literally "unless not?") or simply to the end of almost any statement to verify it and ask "isn't that right?".