macOS built-in spell checker performs badly - what can I do?

macOS Mojave cannot detect that I made a mistake at **badd** and cannot guess that "approximately" was spelled incorrectly. How can I improve the built-in spell checker? (i.e. I don't want to use a spell checker inside Microsoft Word or similar third party application that has its own spell checker) There is a good thread here, but no solution either: https://discussions.apple.com/thread/7502895 I also tried Grammarly . That company promises in tons of online ads that its app and browser extension can help you identify “*errors that other spelling and grammar checkers just can’t catch*.”. “*...First Do No Harm*” would be a better founding principle. IMHO Grammarly is not a good product because it caches many errors that aren't. Take any error-free text and look at what Grammarly does with it. Here, the Universal Declaration of Human Rights: Next I tried SpellCatcherX who was 100 times better when it worked, but it doesn't really work anymore. http://www.rainmakerinc.com/products/spellcatcherx/ What can be done to improve this?