The Doctor's "Language"

So over the past few months I have caught my girlfriend up to date with the current series. And she become a fan of the show.

Today she texted me an interesting question that I had never thought of.

"Big question: Does the Doctor really speak English or is it an alien language, but the TARDIS makes him talk English with a British accent?"

Ive been under the impression that he actually spoke English. But in all fairness its a good question.

Just thought I'd put that out there.