look at the nations today
every country in europe (most of them at least) is the direct result of the borders of a nation state/governement, aka in most cases just the land owned by a random rogue warlord and his army
languages were shaped by governements to match their borders to create loyalty, having a common language creates a bond, a very strong tool of psychological control over normies and the low IQ masses, that language had to be different from those of all other nations, this is why spanish and italian were made different from french, why portuguese was made different from spanish, why danish and norwegian were made different from swedish etc, despite having all been one language in the past
but the golden rule is one language for all of the enslaved subjects of a state, that is different from all other languages. This maximizes loyalty, and the willingness of your slaves to fight the slaves of other nations in your wars.
This is the truth about nationalism, it's nothing but lies, invented by governement as a tool of power over the masses, to make them obedient, and willing to fight their brothers in wars.