Actually the most proposed and welcomed suggestion was 20/25/30/35% discount through the Ages. But imo this still asks for trouble. It’s just like the old AoC Aztec Militia rush all over. You can get at least 1 more militia in the transition or even fully commit to Dark Age fighting with Goths, like Viper showed a couple of times. I think he also did that with Teutons against DauT in some game, it was pretty hilarious.
About your question: The term “unberitten” simply is the original german translation for “Infantry civilization”, teutons (unberittenes Volk) and vikings (unberittenes Volk von Seefahrern - Infantry and naval civilization) also share this term.