Siwss, I'm sure he is referring to the recent Medieval Kingdom Mod that converts Attila into a sort of Medieval II era, working only in custom battle (so only tons of unit names which could be added, meanwhile it shouldn't be possible to add all modifications of factions' names).
At last unit names could be added if they all have total new entries (not sure of this, I don't use this mod) but in any case factions names could not be modified due to overwriting existing entries of the core game.
At last it's better to 1. use the game in english with this mod 2. made a medival Kingdom upc separated from this one: good luck to the one who will do this