Literary and colloquial
Not to bring up a potentially thorny subject, but is the course only literary Czech or are there also lessons dealing with (at least understanding) colloquial Czech?
The last skill of the tree deals with understanding of typical features of Common Czech (https://en.wikipedia.org/wiki/Czech_language#Common_Czech), the most common vernacular (inter)dialect.
All other parts of the tree are restricted to standard (literary) Czech including its "colloquial" or "spoken" form ("hovorová čeština").
Thank you for the link. But after reading it I'm a BIT scared: "Compared to standard Czech, Common Czech is characterized by simpler inflection patterns and differences in sound distribution." "Standard Czech is still the norm for politicians, businesspeople and other Czechs in formal situations, but Common Czech is gaining ground in journalism and the mass media." "Common Czech is characterized by quite regular differences from the standard morphology and phonology. These variations are more or less common among all Common Czech speakers"