Yoruba is spoken by about 30 million people in Togo, Benin, and southwestern Nigeria. Yoruba, together with Igbo and Hausa, are Nigeria's three most widely used languages. Although it has some twenty distinct dialects, standard Yoruba is used in the media, literature, at all levels of education and is understood by speakers of all the various dialects. Little known outside of Western Africa, Yoruba had remained an unwritten language until the early 19th century. In 1819, the first Yoruba word list was published which served to introduce the language to the linguistic community. By the late 1940s, Yoruba became one of the earliest West African languages to have its own written grammar and dictionary. The Yoruba language has been written in the Roman alphabet for over a century. A few diacritics are used to indicate additional sounds which are not present in Western languages, such as to indicate low tones and high tones.