Truth be told, I could not perfectly understand what Kouyou was saying. It was was thanks to the Mystic Code app I had installed in one of my forelocks that I could communicate with her on this level at all. It guessed the general gist of what she was saying, based on samples of previous conversations and interjections from Karin, and showed me what it conjectured to be its broad meaning – effectively, analysing and translating her body language in real time. In Kouyou’s case, I was able to communicate with her clearly and in person, so the translation accuracy was particularly high.
This was one of the problems that came part and parcel with Berserkers, but Karin didn’t seem as though she minded it in the slightest. She had told me in the past that, although she was her Master, even she did not hear Kouyou’s thoughts as human speech; rather, they came to her as wordless ideas.
Incidentally, this app did not work at all on Pran. It had only returned the vaguest of suggestions, so in the end I had removed him from the list of targets.
Fate/Requiem, Volume 1, Chapter 2