I noticed the Roman dynamic name for the Netherlands in-game is 'Netherlands instead of the historical 'Belgica'
Possible Roman Dynamic Vassal Names. This also includes names for new civs:
Aztecs: Anahuac
Modern Mexico: Mexicum
America: Novi Orbes (New World) - this might sound silly but it was taken from an
original source.
Canada: Ultima Thule or
Hyperborea - it seems fitting that this could be name of Canada since Utima Thule was used in middle ages to mention far away places.
Hyperborea was meant to be north Eurasia but I could easily see that transferring over to Canada if/when its discovered.
Colombia: Musica (native name)
Incas: Cuscoa (native name)
Brazil: Pindorama (native name)
Argentina: Ultima Thule Meridionalis (fictionalized name based on Thule and Argentina's Southernmost position
Congo: Asigyama
Indonesia (Java): Insulinda
Celts: Gallia Celtica
Vietnam: Manzi (After Marco Polo's description of Southern China)
Nubia: Aethiopia? or...
Nubia: Aethiopia Superior
Ethiopia: Aethiopia Inferior (if somehow these two are vassals at the same time)
Sweeden: Suecia
Assyria: Should be Assyria?
Sumeria: Mesopotamia
Malaysia: Aurea Chersonesus
Khmer: Kattigara (or Aurea Chersonesus if no other southeast asian civ exists)
Swahili: Azania
Hittites: Cappadocia?
Kieven Rus: Bospora or Scythia
Chola: Taprobane
Myanmar: Besynga
Toltecs: Columnae Tula (Pillars of Tula)
Maya: Either Itza being the name of the people of Chichen Itza or something fun... given the mythological nature of Mayan Civilization and its distance from Rome I think calling it Elysium would be a wonderful easter egg but I don't expect that to go anywhere.