"Gutenschwarzen" is not an actual german word but would translate to something like "good black".
When Chris' German girlfriend asks if he's ready to go, he answers "Hell, da!" "Da" means yes in Russian.
When Peter's twin regenerates he says "My name is Retep and I am evil". "Retep" is "Peter" spelled backwards. This serves as a trope regarding direct opposites of main characters (especially in action movies or series). Being the opposite (evil, in this case) of Peter is foreshadowed by the reversed name.