Does leteroj mean letters as in the symbols in words or the type of mail?
letero—the thing that comes in an envelope delivered by your friendly neighborhood postal worker.
Ne skribu al mi tiajn longajn leterojn.
litero—symbols in words
La 28 literoj de la Esperanta alfabeto estas a, bo, co, ĉo, do, e, fo, go, ĝo, ho, ĥo, i, jo, ĵo, ko, lo, mo, no, o, po, ro, so, ŝo, to, u, ŭo, vo, zo.
No problem. You can always make the suggestion that an answer is actually correct. We all work together here! I actually got one of my corrections approved :)
Esperanto word order is very flexible do to the accusative suffix -n. I haven't found a sentence structure from any language that I cannot duplicate in Esperanto. This language is very expressive!
It did ages ago, but it was persecuted by the Nazis during World War II, thus the decline. In Nazi Germany, there was a motivation to persecute Esperanto because Zamenhof was Jewish. In his work, Mein Kampf, Adolf Hitler specifically mentioned Esperanto as an example of a language that could be used by an international Jewish conspiracy once they achieved world domination. (source)
The -n suffix is the indicator of the accusative case, so Leteroj is used when it is the subject of a sentence. Leterojn is used when it is the object.
In languages where the word order is more rigid (like English), it isn't as important to indicate the case, since you can tell by where it is used in the sentence; however, there are a few times where we do indicate it. For example, I/me, we/us, he/him, etc.