You're not the only one to express that concern; so there's probably more than a grain of truth to it.
I'd tried to establish that Missy knew random bits of obscure languages in chapter 54, "Vocabulary". I also have a full intention of describing the rationalist reason for Missy knowing such random trivia, exemplified by my very username, or as it was put in HPMoR's chapter 26, "one of the requisites for becoming a powerful wizard is an excellent memory. The key to a puzzle is often something you read twenty years ago in an old scroll, or a peculiar ring you saw on the finger of a man you met only once."
I have chapter 68 mostly written out, chapter 69 mostly plotted out, and a roadmap of points I want to hit in the next few chapters. One of those points happens to be able to be used as an excuse to go into more detail about Missy's background, including why she knows some of the seemingly random things she does - so if I work it right, I should be able to provide a resolution for your criticism in chapter 70 or so. I hope that you find it both acceptable and enjoyable.
For the past two months, I've been writing, and posting, roughly two thousand words a day of "Myou've Gotta be Kidding Me", a story set in a "My Little Pony: Friendship is Magic" fanfic universe, "Chess Game of the Gods". Outside of the sheer NaNoWriMo-like exercise of pushing out near-daily chapters, I've also been trying to keep in mind the various principles I've learned from Yudkowsky and LessWrong, and to try to present them in a way that people who like reading MLP fanfics might be able to appreciate.
I've just come to something of a minor climax with chapter 60, and while I'll definitely be continuing the story, this seems like a good time to mention it here, for whatever feedback and constructive criticism anyone cares to offer.