Czech is actually the official language spoken in the Czech Republic. It is a Slavic language and is closely related to Slovak, Polish and Serbian. Czech has undergone some evolution as a Slovak language. Although it sounds complicated, it is an Indo-European language, just like English and German.
There are several dialects of the language, but the four main ones are the Bohemian-Moravian, Central Moravian, Eastern Moravian, and Silesian. The differences are, however, not so significant. Although the Czech Republic is considered a small country, the language has over 10 million speakers, making it more prevalent than most people think. It is, however, known to have a very complex grammatical structure.