Did you install any new fonts, do anything to any system fonts or in general do you have a lot of added fonts?
Time for some
font troubleshooting. First - disable all fonts you have added with Font Book or other software, then log out and back in. If it looks correct now, it's one or some of your fonts that are acting up. Either validate them, or disable/enable 50 % of them at a time until you find the bad ones.