If you're having problems like in the image below, it could be caused by corrupt font cache files. What appears to be happening is that incorrect or corrupted encoding vector information is being used when mapping the character codes as input by your keyboard to the glyphs they represent in the problematically cached font.
You can use Font Finagler's Font Cache Cleaner feature to purge these cache files in an attempt to restore normal behavior, and to help rule out a font cache corruption as the sole cause of the problem. If, however, you use Font Cache Cleaner but the problem remains, then it could be caused by a font conflict, by a corrupt or less-than-ideal-quality font, or by an underlying OS X font-handling bug. Try removing fonts to isolate the problematic fonts that are causing this behavior.
Read more >>