arabic
Abd al Mallik unify the empire by making Arabic the official language of government in all Muslim lands
The official language of Songhai is Muslim.
Latin was the official language.
Turkish
They spoke the over 9000 language of dank memes lord, pepe the frog.
The official language in the western Roman Empire was Latin. Latin was also the official language of the eastern part of the Roman Empire, together with Greek. This was because it was the language of the Romans.
Arabic
High German was the official language of the Austrian Empire as early as the 1300s and remained the official language of Austria continuously since then, including during the reign of the Habsburgs.
The introduction of Arabic language united the Mulims of different areas together.
The official language of the Parthian Empire was Parthian, which is a Middle-Iranian Language (whereas Farsi is a Modern-Iranian Language). Aramaic was also commonly spoken as a vernacular in the western part of the Empire.
Typically, the official language in the Caliphates was Arabic, but there were several Caliphates in Persia, Central Asia, and India which did not use Arabic as their official language. The Ottoman Empire also used Turkish.
The official language of the Roman empire was Latin throughout its history, including theHellenisticperiod. Local peoples spoke their own languages.