Common language in a nation? Just look at India. There are no common languages no matter how much the state tells you the official languages are Hindi and English but everything is translated into regional languages anyway because the vast majority speak neither of those.
maybe u cannot call them a nation. I dont know about india so I w,ill not talk about them before I learn some but see north africa please. they mainly talk arabic and you cannot call them algerian, moroccon, tunusian, libyan, egyptian but arabs.
also u can see turkish world. we(in turkey) call khazaks, azerbayjanians, turkmen, north cyprussian, ozbek, kirgiz, karaçay-çerkez federal government, kabartay balkar federal government, tatars, baş kurdistan federal government, çuvaşistan federal government and dagestan federal government turks first. Turkish people are Turks, Khazaks are Turks, etc... And after Soviets brought Russian language to Khazakistan, you see Khazaks are becoming Russian in a time.
As a result, Language--->Culture--->Nation
PS: You cannot call Greeks, under Ottoman Empire as ''Ottomans or Turks'', they are Greek.