It has been recorded before, speaking with a foreign accent but not speaking a foreign language that you have never spoken before, that, I think, is impossible.
It has been recorded in people with brain injuries or traumas.
On the lighter side, I took my niece to Paris when she was 12/13 and she spent the week talking english with a french accent.
She thought it meant she was speaking french, I felt like I had Peter Sellars' Clouseau avec moi, it caused much merriment.
Not now Kato. 
