In italian we would say le lettere sono lunghe. so the equivalent of something like "laj leteroj iliestas longaj", everything in the plural and the verb conjugated to the third person plural.
But the thing is changing everything but article and verb... I wonder if there are other languages that behave this way.
I mean romance languages behave like Italian so they all change both the articles and the verbs. English has only one form for both articles and adjectives. The scandinavian languages have articles as suffixes just most balcanic languages: Romanian, Albanian, Macedonian and Bulgarian. Hungarian has never-changing articles, but then the adjectives change only when predicative, never when attributive. In Dutch the masculine article never changes, but then there's another article and adjectives in the predicative form don't change; in this it is similar to German, that has richer variety in both article and adjective declension. The slavic languages don't have article apart from the aforementioned.
I really can't think of any other languages behaving like Esperanto.
The previous lesson taught us that direct objects - not plurals - end in "n." An object of a sentence is the thing that receives the action of the verb - in the sentence "I picked up the letter," the object is "letter." As taught in this lesson, plurals end in "j."
Hope this helped!