The article brings a comprehensive knowledge of the language situation in the Czech lands during the reign of the Emperor and King Charles IV, whose 700th anniversary of birth was commemorated by the Czech Republic in 2017. The author focuses primarily on the relationship of Charles IV. to the Czech language and to other languages, and describes the periodic language situation in the Czech lands as well as in the Holy Roman Empire, ie the coexistence of Czech, German, Latin and Old Slavonic.