Esperanto is the most widely used constructed language intended for international communication; it was designed with highly regular grammatical rules, and as such is considered an easy language to learn. Each part of speech has a characteristic ending: nouns end with ‑o; adjectives with ‑a; present‑tense indicative verbs with ‑as, and so on. An extensive system of prefixes and suffixes may be freely combined with roots to generate vocabulary, so that it is possible to communicate effectively with a vocabulary of 400 to 500 root words. The original vocabulary of Esperanto had around 900 root words, but was quickly expanded. Source: Wikipedia (en)