These lines just indicate the the locale gedit was trying to use aren't supported by your C library.
(process:2629): Gtk-WARNING **: Locale not supported by C library.
Using the fallback 'C' locale.
gedit should have continued to start up. Did it? If so, can you use it?
You said you had no idea what you had done. Welcome to the world of 'I did something maybe' but I've no way of remembering <GRIN> Happens to me alot. When I encounter situations like this I try to remember what I was playing around with. If you can remember even partially what you were doing, someone might see what the problem is. By the way, I am assuming gedit wasn't giving these warnings before hand.