Languages of the Ottoman Empire
The language of the court and government of the Ottoman Empire was Ottoman Turkish, but many other languages were in contemporary use in parts of the empire. Although the minorities of the Ottoman Empire were free to use their language amongst themselves, if they needed to communicate with the government they had to use Ottoman Turkish.
Firman of Karamanoğlu Mehmet Bey
Agop Dilaçar, who is known for his works on the Sun Language Theory, claimed that Mehmed Bey might have declared Turkish the official language of the state. According to Dilaçar, in his firman dated 13 May (15 May ?) 1277, he ordered that "from that day forward, in the council, in the dervish lodge, in the court, in the assembly, in the square, no language but Turkish should be spoken".
Before him, the Seljuq elite in Anatolia used Persian in literature and Arabic in government and science. The Turkmen, however, could not understand these languages.