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.
Turkish vocabulary
When the Ottoman Empire arose out of the remains of the Selcuk Empire in Anatolia, its official language, "Osmanlıca" or Ottoman Turkish, became the only language to approach English in the size of its vocabulary (according to #Lewis). However, common people continued to use "kaba Türkçe" or "rough Turkish" which contained much fewer loanwords and which is the basis of the modern Turkish language.