Learn Farsi: کاش همه‌ی مردم خوشبخت زندگی می‌کردند.

After کاش (I wish), Farsi uses the past continuous tense to express a present unreal situation. This means you are wishing for something to happen right now that isn't actually happening. It's very similar to English, where we also use a past tense form for present wishes ("I wish they lived happily").

Does مردم (people) always take a plural verb ending like -ند (-and)?

Yes! Just like in English, the word مردم is grammatically plural. Even though it doesn't have a regular Farsi plural suffix like -ها (-hâ), it always takes a plural verb conjugation. That's why the verb is می‌کردند (they did) instead of the singular می‌کرد.

Why does همه (all) have a ی attached to it?

The word همه (all) is linking to the noun it modifies, مردم (people), so they need to be connected by the ezâfe. Because همه ends in a silent 'h' (ه), the connecting ezâfe must be written with a ی to create the "-ye" sound, making it همه‌ی مردم.

The word خوشبخت is an adjective meaning happy or fortunate. How does it act as the adverb happily here?

In Farsi, you can frequently use an adjective directly as an adverb without changing its form or adding any special endings like English does with "-ly". Placing خوشبخت directly before the verb phrase زندگی می‌کردند tells us how they are living.