Character mistake: The leader of the Purple Knights says that they would only be bike riders if they couldn't tell which gender someone was by their hair. This is a major mistake, because if you look at the hair of the Purple Knights, it's incredibly easy to tell which gender someone is.
Character mistake: Season 2, Episode 27 'Pussycat Galore' :Maxwell translates his famous line "And loving it' into the German 'Und damit gefreut'. Agent 99 who claims to speak German fluently confirms it. This translation is both far away from the meaning and doesn't make any sense at all. The right translation is 'Und liebe es'.