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.
List of lingua francas
Persian became the second lingua franca of the Islamic world, in particular of the eastern regions. Besides serving as the state and administrative language in many Islamic dynasties, some of which included Samanids, Ghurids, Ghaznavids, Ilkhanids, Seljuqids, Mughals and early Ottomans, Persian cultural and political forms, and often the Persian language, were used by the cultural elites from the Balkans to India. For example, Persian was the only oriental language known and used by Marco Polo at the Court of Kublai Khan and in his journeys through China. Arnold Joseph Toynbee's assessment of the role of the Persian language is worth quoting in more detail:
In the Iranic world, before it began to succumb to the process of Westernization, the New Persian language, which had been fashioned into literary form in mighty works of art ... gained a currency as a lingua franca; and at its widest, about the turn of the 16th and 17th centuries of the Christian Era, its range in this role extended, without a break, across the face of South-Eastern Europe and South-Western Asia.
Persian remains the lingua franca in Iran, Afghanistan and Tajikistan.