Stefan has given you the link. I guarantee the answer is there.

To check your proofing language, type a misspelled word that doesn't get flagged. Select it.

Then under the review tab click on Select Language. Look at the bottom to see if "Do not check spelling or grammar" is checked. I know you checked language, but do it this way if you did not do it this way before. The proofing language is a type of character formatting.