By trivias, I basically mean things that even those who have finished and got all 4 endings of Nier didn't or don't know about yet. These are the trivias I know about:
-Popola and Devola share the same voice actress, the same VA voices both of them in both English and japanese (ryoko shiraishi/eden riegel)
-Weiss is German for white, so Grimoire Weiss means "white Grimoire"
-Noire is French for black, so Grimoire noir means "black Grimoire"
-Nier is French for "denying"
-father Nier shares his birthday with nowe (from drakengard 2) and his birthday is the same day as the release date of the original drakengard game for ps2.
-brother Nier shares his birthday with the creator of the series, yoko taro.
-In a DLC released for the game (known as the world of recycled vessels for gestalt version, and 15 nightmares for replicant version) you can play as the other version's Nier (brother Nier in the gestalt version and father Nier in the replicant version) for a short period of time.
-in drakengard 1 and 2, there is a weapon called skald's song, however it's name in the japanese version is "devolapopola", so that's where yoko taro probably got the name for the sisters in Nier, in fact, the drakengard datebook mentions that Mr taro liked the story of the weapon and wished to make the sisters characters in one of his future games. In fact, while the weapon's history is different in drakengard 1 and 2, both games' tale of the weapon has a similarity, both games say that the weapon was forged by two twin sisters.
-kaine is voiced by atsuko tanaka in the japanese version, she is particulary known for the fact that she voices rough, tomboy, and typically violent women (e.g trish in devil may cry Anime and MvC 3, Bayonetta, konan in naruto, lara croft, lisa lisa in jojo's bizarre adventure, etc)
-in the second Playthrough of the the game, in kaine's story, it is implied that she is a hermaphrodite/intersex, specially one part that says that the villagers viewed her as a freak long before the shade got inside her, and that a boy also told her "why do you dress like a girl? We all know what you really are!"
So, what trivias do you know?