Esperanto advocate Leo Tolstoy claimed to have learned it in four hours. Most linguists class it among the easiest languages to learn, especially for Indo-European language speakers. Though not an official language in any one country, Esperanto has been recognised by the French Academy of Sciences and UNESCO, and now has an estimated 2 million speakers worldwide. Created in the late 19th century, this nationally and politically neutral language was constructed for easy acquisition. What makes this man-made language so simple to learn? The spelling system is regular and phonetic, and the rules of grammar are simple and designed without irregularities. Words are constructed building-block style out of regularised prefixes, roots, and suffixes. Words compound logically, as we see in birdokanto (birdsong), akvobirdo (waterfowl), akvomelono (watermelon).