I StumbledUpon a page that listed a bunch of 'bizarre mental disorders'. In the list was Foreign Accent Syndrome. It is a rare medical condition (mostly brought about due to injury), which causes the afflicted to speak their native language with an (apparently) foreign accent. There have been 50 recorded cases of this.
I guess the key word here is 'recorded'. If we were to record cases, then there would be a few hundred thousand (if not million) cases in India alone. And the condition wasn't brought upon them by trauma. A short visit to any natively English speaking country (US, UK etc) seems to be 'injury' enough. ;-)