Is it possible to disable spell check systemwide?
Renaming '/System/Library/Services/AppleSpell.service/Contents/Resources' did not work for me since that file doesn't seem to exist on this install (10.11). What did work was disabling it for the languages I usually write in, under System Preferences->Keyboard->Text->Spelling select menu. It's set to 'Automatic by Language' by default, choose 'Set up…' at the bottom and deselect your languages. Restart the applications that use the Spelling service.