Based on a tumblr text post.

The Doctor emerged from the lower part of the console room, where the work was done. Martha walked into the console room as he climbed the stairs.

"Well, it looks like the translation circuit is broken," the Doctor said, but Martha didn't understand.

"I'm sorry? I don't understand, what language are you speaking?"

"What? Oh, sorry, force of habit. I was speaking Common Gallifreyan. I know English, almost fluent enough to fool a native speaker, but it's just loads easier to speak in my native tongue, you know? But I said the translation circuit is broken. It usually takes care of the language barrier," the Doctor said. Martha understood this time, laughing a bit.

"Ah, I see," Martha said.

"Wha-what you laughing at?" the Doctor said, an odd inflection in his voice.

"You've got an accent! Nothing close to that London accent the translation circuit gives you!" Martha said.

"Oi, it's not funny!" the Doctor said, his accent giving the word 'funny' an odd sound. Martha couldn't stop laughing.

"Fine, I'm going to fix the translation circuit," the Doctor said grumpily, going to the lower part of the console room to fix the part, leaving Martha keeled over in laughter in the chair next to the console.

The Doctor had the part fixed in about an hour, giving Martha enough time to calm down.

"Is that better, Martha?" the Doctor said, his normal accent back to normal.

"Loads."