Learn Spanish (Latin America): La cena de cumpleaños fue especial.

You would say ¡Qué cena de cumpleaños tan especial! or ¡Qué cena de cumpleaños más especial!. To make this kind of exclamation in Spanish, you place the noun (cena de cumpleaños) between qué and tan (or más) before adding the adjective (especial).

Why does this sentence use fue instead of era to describe the dinner?

While era (the imperfect tense) is often used for past descriptions, fue (the preterite tense) is used here because the dinner is an event that was completed. Using fue especial sums up the whole event after it finished, rather than describing what it was like while you were in the middle of it.

Why is it cena de cumpleaños instead of cumpleaños cena?

English lets you put nouns directly in front of other nouns to describe them (like 'birthday' describing 'dinner'). Spanish doesn't allow this. You have to use de (of) to connect them, making it literally 'dinner of birthday'.

Is cumpleaños plural here because it ends in an 's'?