Learn Arabic (Modern Standard): ليت الزرافة سريعة مثل الغزال. - I wish the giraffe was as fast as the gazelle.

In English, we use the past tense ("was" or "were") to express an unreal wish about the present. In Arabic, you simply use a verbless nominal sentence after ليت to express a wish about the present state of things. Adding a past tense verb like كانت here would change the meaning to wishing about the past.

How does the word ليت affect the grammar of the noun that follows it?

ليت is one of the "sisters" of إنّ. This means it changes the subject of the nominal sentence, الزرافة, into the accusative case (mansub), giving it a fatha ending. The predicate, سريعة (fast), remains in the nominative case (marfu).

The English translation says "as fast as", but how is that comparison structured in Arabic?

Arabic does not have a direct structural equivalent to the English "as [adjective] as". To make this kind of comparison, you simply state the adjective and follow it with مثل (like). Literally, the end of this sentence translates to "fast like the gazelle."

What grammatical case should الغزال take after مثل?

It takes the genitive case (majrour). This is because مثل acts as the first part of an idafa (possessive construction) in this context, forcing the noun immediately following it into the genitive case.