As it was already stated, GRRM was mainly taking English names and transforming them. He also took some names from other places, like Elmo and Kermit, or the Valyrian names (I have no idea if he stole them from somewhere or invented them himself). Comparing AGOT cultures to real ones isn't a good idea. Andals and the First Men would be English. Well sure, you can try to find rferences to the Wildlings, Rhoynars, Valyrians, Ghiscarians, Yi Tiyans, Lengians, Asshaians and all that stuff. But is their language similar? You don't know.
You could use, like, Scottish Gaelic for the Wildlings, or Scottish for the Northmen, but this wouldn't be accurate, would it?