Czech (/tʃɛk/; čeština Czech pronunciation: [ˈtʃɛʃcɪna]), historically also Bohemian (/boʊˈhiːmiən, bə-/; lingua Bohemica in Latin) is a West Slavic language of the Czech–Slovak group. Spoken by over 10 million people, it serves as the official language of the Czech Republic. Czech is closely related to Slovak, to the point of mutual intelligibility to a very high degree, as well as Polish. Like other Slavic languages, Czech is a fusional language with a rich system of morphology and relatively flexible word order. Its vocabulary has been extensively influenced by Latin and German. The Czech–Slovak group developed within West Slavic in the high medieval period, and the standardization of Czech and Slovak within the Czech–Slovak dialect continuum emerged in the early modern period. In the later 18th to mid-19th century, the modern written standard became codified in the context of the Czech National Revival. The main non-standard variety, known as Common Czech, is based on the vernacular of Prague, but is now spoken as an interdialect throughout most of the Czech Republic. The Moravian dialects spoken in the eastern part of the country are also classified as Czech, although some of their eastern variants are closer to Slovak. Czech has a moderately-sized phoneme inventory, comprising ten monophthongs, three diphthongs and 25 consonants (divided into "hard", "neutral" and "soft" categories). Words may contain complicated consonant clusters or lack vowels altogether. Czech has a raised alveolar trill, which is known to occur as a phoneme in only a few other languages, represented by the grapheme ř. Czech uses a simple orthography which phonologists have used as a model.