Just click the "do not check spelling and grammar" box until it is completely clear, and that will remove the "do not check spelling and grammar" formatting regardless of which languages are applied to the text, and will not change your language formatting. If your document uses more than one language, when you Select All and go to Tools>Language, you will see that no language is highlighted. If the “do not check spelling or grammar” box has a dash in it, this means part of your text is tagged “do not check.” Click twice to clear completely. Be sure to Select All the text first! Now it should work. Select all the text, go to Tools>Language, select the desired language, uncheck the “do not check spelling or grammar” box if necessary, and hit OK.
New documents will behave, although you will need to fix old documents one-by-one. Then anytime you use that style in the future, it will automatically have the language tags. You need to modify the style that the text is formatted in, to include the language formatting. Fixing All Documents, or Changing the Default Language Spelling depends on the language setting, so first make sure you have a Tools>Language menu entry. Note: the Word 2004 Help topic "Troubleshoot spelling and grammar checking" also addresses some questions not covered here. Tools>Spelling & Grammar Dialog Stops Showing Suggestions.Spanish Custom Dictionary-FIXED with Office 2004 SP2 (11.2).There Is No "Language" on My Tools Menu.The Spelling & Grammar Preferences Are Grayed Out.Change Language in a Single Click in Word 2008 (external link, scroll down for English).Spell-Check Doesn’t Catch Misspelled Words.Updated for Word 2008 (DRAFT in Progress) You can also add new automatic corrections for words you commonly mistype or remove words you do not want automatically corrected.Spell-Checking, Language, and Dictionary Issues in MacWord You can also add new automatic corrections for words you commonly mistype or remove words you do not want automatically corrected. Click the Office button in the top-left corner.Click Options in the left navigation pane.
If the box in unchecked, the feature is disabled. If the box is checked, the feature is enabled. On the AutoCorrect window, you can disable features you dislike, such as the auto capitalization of first letters of sentences, or disable AutoCorrect all together. In the Word Options window, click the Proofing option.