I installed CocoAspell to help with spellchecking TeX documents (TeXShop). I liked the concept but I did not find it particularly helpful, and I preferred the native Apple spellcheck (despite underlining the TeX commands).
But after i uninstalled it, the English dictionary in Spelling did not work (in any program, such as TextEdit, Mail, etc.). The other languages worked fine (red underlines, and so on), but English did not. Eventually, after much troubleshooting, I simply deleted the AppleSpell.service file from the system/library/services folder and reinstalled the one from my other Mac. It now works fine. I just wanted to provide this feedback in case anyon else has similar problems.