Czech is the main language in the Czech Republic, spoken by around ten million people. (Minority languages here include German, Polish and Romani, but Czech is the native tongue of the overwhelming majority). It is a Slavonic language, very closely related to Slovak (Czechs and Slovaks understand one another with little difficulty), and similar to Polish and Russian. Although Czech may sound baffling to many a Western-European or American visiting the Czech Republic, it is an Indo-European language like French, German or English.
If you are familiar with Latin, then Czech grammar won't seem unfamiliar, especially its complex system of different noun cases, which are very intimidating to many learners of Czech.
It is hard to say precisely how old the Czech language is, but it is known that Slavs first settled this part of Europe around the sixth century, and the first written Slav language here was Old Church Slavonic, brough in the 9th century by the two Byzantine missionaries, Cyril and Methodius. But the main literary language for most of the Mediaeval period was Latin.
Czech gradually developed as a distinct language and there are still many texts surviving going back as far as the late 13th century. Czech culture blossomed under the 14th century emperor, Charles IV, but faced turbulent times with the Hussite wars that came soon afterwards. With the onset of rule by the Austrian Habsburg dynasty, Czech went into decline as a written language, with German becoming the language of the elite. Czech remained the language of the countryside. To this day the German influence can be felt strongly in the Czech language. It was not until the second half of the eighteenth century that deliberate attempts began to reverse the decline of the Czech language. With the national revival movement of the 19th century, Czech rapidly gained ground in most areas of education and public life. Prague's National Theatre built on the banks of the River Vltava is probably the most potent symbol of this revival, which culminated in 1918 with the collapse of the Habsburg Empire and the foundation of the Czechoslovak Republic. Although Czechoslovakia was a multi-lingual country, with three million German speakers, a similar number of Slovak speakers and around a million Hungarian speakers, Czech was the dominant language of the administration. During the Nazi occupation in the Second World War, German again became the official language. For example all street signs, official documents and banknotes were first in German, then in Czech. The mainly German-speaking border regions were annexed by Germany. After the war Czech again came to the fore.
Under communist rule - from 1948-1989 - the authorities often used the Czech language as a political tool, putting great stress on its similarities to Russian. Since the fall of communism the pendulum has swung the other way. There has been a dramatic increase in the number of Anglicisms in modern Czech, many connected with the world of business, retail, computers or popular culture.