Esper/Welcome to the book Esper
The Esper' language is a very regular language. In fact, the primary rule of Esper' grammar is that there's no such thing as an exception. What you can do to one word, you can do to ANY word. Of course, this does not mean that all words will cooperate well with this rule. For example, adding an "n" to the end of a word which already ends in "n" may produce something which the speaker might find difficult to fathom how to produce distinctly... but if you can add an "n" to the end of one word, you can add it to the end of another as well, with the same "grammatical effect" intended, and not have to worry that doing so may be "wrong" for some reason you have not yet learned.
For example, in English the word "person" has three plural forms. There is the irregular plural "people" which refers to multiple individuals taken as a whole, the alternative but regular form "persons" which tends to refer to the number of individuals, and the dual-plural "peoples" which speaks of the number of "whole groups" of persons, but in the English language such a case is considered an "exception" and you can't expect other words to have such flexibility.
In the Esper' language, you can say "ulo" to mean Person. Esperanto speakers will recognize that form right away, as will speakers of several other languages, and in fact the Esperanto word "persono" which also means "person" but in a slightly different sense, is also an Esper' word with the same meaning. But sticking to forms of the word "ulo" for this lesson, we can form the standard (and REGULAR) plural "uloy" to mean "people" which again, any Esperanto speaker will recognize right away. We can also form the alternative (and ALSO REGULAR) plural "iulo" which means "persons" and the dual-plural "iuloy" which means "people". The solution for these four forms in most languages is the same as in English... irregular. In fact, in Esperanto, "popolo", which you may recognize as related to the English word "population", is one a singular word often used to represent the plural idea of "people".
In fact, the flexibility of the Esper language in expressing various forms of and variations on the "plural or singular" concept doesn't stop there. The prefix "i" roughly means "some" and can be replaced with "on" to mean "one". That's right. The word "ulo" means "person" but is a number ambiguous word, rather than a "singular" word. If you want a word to be "specifically singular" in the Esper' language, you can say so. This also allows for single word disambiguation of similar concepts such as "one people" (onuloy), "one or more peoples" (iuloy), "no peoples" (neniuloy) "zero peoples, and so on.
Now, I said in the Esper' language you can do the same to any word, but that the words may not always cooperate. How about I take a simple example. The Esper word "mi" means "I" or "me" or in other words, the person doing the speaking or writing. The "first person" pronoun. The "i" ending is an "infinitive proform" ending, which can indicate an infinitive verb or a proform, which may be taken as a pronoun or some other kind of proform, depending on the context. Easily enough we can form "imi" to me "us" or "we" and it is no trouble in written or spoken form, and in fact that is the "standard" way of forming plurals for proforms in the Esper' language, but if we form "miy" as the "alternative plural" some people may find it hard to pronounce, or difficult to distinguish when listening, depending upon how the speaker is accustomed to pronouncing the letter "i" which should be treated as a single sound without changing from word to word, but can range within the Esper' language from the English "long e" sound as in the word "seen" to the English "short i" sound as in the word "this". As a result, the alternative plural of proforms is not encouraged, but it is also not "wrong" and may be used at one's discretion.
As a point of clarification, this textbook is intended at its inception to be a LEARNING resource, rather than an authoritative reference resource. Think of it as more are than science. This is not to say the "science of language" can't be covered in this book, but rather that "society as a whole" should have the real say on finer details of the Esper' language and its translations to and from other spoken and written languages... not this book.
Every aspect of human language phenomena is constantly evolving, so don't expect to find "the translation" for a word in here, to or from ANY language, but please do enjoy learning what you can from this book and perhaps adding something of your own potentially helpful insight on this open source language.