There already is a suggestion to Please add a spell checker to the Markdown editor, but since that is solved better by the browser itself, I suggest this:
There is a lot of work involved for moderators to simply correct spelling. This could be minimised if SO would better warn before posting a question with lot of spelling mistakes.
I know, there is already the message, if something is wrong:
This question body does not meet our quality standards. Please make sure that it completely describes your problem - including what you have already tried - and is written using proper grammar.
At first, I could not submit this question at Stack Overflow, because of this warning. That is fine. Then I added some more correctly spelled text and the warning was gone. Although there are a lot of mistakes still.
There should be a dismissable warning, if your question still contains spelling mistakes, like
Submit anyway. The mistakes are made on purpose.
This message should only come, if there are still spelling mistakes left, although the current checking algorithm said it would be ok.
Related idea: Is it time to do something about spelling and grammar?