I love Doctor Who; it's one of my favorite shows. I've watched every episode that has come out in the past ten years at least once, and twice for several seasons. I've always found one thing interesting, however: there's never any period-accurate English. After all, I'd think that the English would have been slightly different when the Tenth Doctor and Marsha went and visited Shakespeare, or when they met Charles Dickens.
I finally figured it out. The answer is simple; in fact, so simple that I felt like a moron for not figuring it out before: the T.A.R.D.I.S. translated it. Remember, the T.A.R.D.I.S. mainframe translates alien languages, except for Gallifreyan. It makes sense that, being a time machine, it can translate language from various time periods as well. But wait! While this solves why there isn't any period-accurate English, it led me to realize something else about the language
of Doctor Who:
The T.A.R.D.I.S. Allows the Doctor To Speak All Languages
Who could forget the self-named Stormageddon, Dark Lord of All? The Doctor doesn't only speak baby, however; consider him barking with Doris at the Rings of Akhaten as the Eleventh Doctor, or the Tenth Doctor talking with the fly people in the Doctor Who special "Planet of the Dead." It could be that the Doctor has managed to learn every single alien language there is, given the fact that he has a time machine (which could explain the Ancient Marshian in "The Waters of Mars") and his age of roughly 1200 years, give or take a couple of centuries. But I don't think even the Doctor is that smart. Rather, I think it was the T.A.R.D.I.S. Consider that the T.A.R.D.I.S. is a sentient being with a telepathic field, which is what translates the languages in the first place. The Doctor is also telepathic; not on the level of the Ood, but he can enter your mind. The theory is this: the Doctor has been in the T.A.R.D.I.S. for so long that the telepathic bond between him and Sexy has strengthened to the point that the Doctor can translate any language, no matter how close his is to the T.A.R.D.I.S. - both geographically and chronologically.
Those are the theories - the T.A.R.D.I.S. has the ability to translate languages through time periods as well as the language itself, and the Doctor and the T.A.R.D.I.S. have a powerful telepathic bond that allows the Doctor to speak and translate any alien language. What do you think?