All characters © BBC
Summary: The Doctor knew nine billion different languages. That didn't dictate that he was a master of communication, by any means.
Amelia Pond didn't even try to understand the TARDIS's translation circuit. Doing so would make her head hurt even more than it did already from trying to decipher the Doctor's incessant ramblings. And those were in English.
Last week they had visited the Kilfrakkans, who had five lungs. The Doctor had employed the use of a little portable translator that looked more like a Gameboy than anything—not because the translation circuit was not working, he claimed, but because most Kilfrakkian inflections had to be made with a specific lung set or the meaning could come out completely different and potentially offensive.
The day after (two hundred years earlier, if you wanted to get technical) Amy heard raw, untranslated Chlastifiggipietran, which the Doctor could only describe as an odd combination of double-tonguing and backwards Aramaic. He claimed the TARDIS couldn't translate it because she would start laughing every time she tried. Amy's iced tea, which had soon found itself meeting the front of her shirt via her nose, could account to that.
The Doctor even knew Beluga Whale, which Amy found the most amusing of them all. Don't ask. Apparently, Earth whales were the most telepathically advanced mammals on Earth besides those of the homo sapiens persuasion, discrediting the dolphins (although no one would ever know). They communicated through a series of songs and acute cryptophasia, which required beings of a higher telepathic level than a human to fully comprehend.
Aside from those few exceptions, Amy found she could understand almost any alien in any language. It was all pretty cool, once you decided to sit back, enjoy the ride and not wrap your head around it.
"Why don't you speak Gallifreyan?" she asked the Doctor on one occasion where there had been nothing better to do. "If, by some weird chance, we met a Time Lord, you two would speak it, yeah?"
The Doctor had been unscrewing the unfortunately broken asteroid trams on his console at the time. Without looking up he replied, "No, we wouldn't."
"Why's that, then?"
The Doctor shook an errant fringe out of his eyes and sighed, finally straightening up to look at Amy. "The words of Old High Gallifreyan hold tremendous power," he said. "They best not be spoken aloud anymore." And that was that.
Although Amy had wondered more about the subject since then, she never asked the Doctor about it again. This was because, as she dutifully reminded herself, the Doctor's secrets were doors belonging to him alone and were not always hers to open.
The Doctor knew most of the languages in the universe, save for the ones that were too old, too simple or complex, or just plain unspeakable. He could fain tell any aggressive species "my ass is coming for you" in nine billion different ways. He'd read every dictionary out there: Miriam-Webster, Oxford, Zxfrujis, you name it. He knew the shibboleths of every planet in the Belt of Negleckt, and he could sing out diphthongs and tripthongs and dodecathongs with the ease of a native, if you asked him right.
He also knew over fourteen hundred ways to artfully dodge a question. Amy had seen it countless times (because, contrary to what the Doctor probably believed, she'd witnessed a whole lot more than the planets and the rainbows of galaxies). The tightening of his mouth. The crinkling of the brow. The way he suddenly found something else to busy himself with or resorted to some facetious gesture that distracted you completely from your train of thought. There was also the blatant subject-changing or the sometimes harsh boomeranging of the question right back at you, if the question being asked was too personal for his taste. Subtle thy name was not the Doctor.
Amy had once asked him about his mother and had received a response of: Did you know that the leaves of an Elebome tree actually secrete a gas that defies the gravity of the surrounding area and makes the trees grow sideways? It's absolutely fan-TASTIC for bungee jumping...
Sure, the Doctor spoke everything. But sometimes he decided to talk of other things. Sometimes he would remain silent and flick his screwdriver to punctuate the quiet.
Sometimes he would smile and laugh it off and wring his hands as if to say, the answer's not important. Why ask me?
And sometimes those green eyes of his looked so sad.
Amy knows, perhaps better than the Doctor himself, that you don't need language to communicate.