*Normally people need this when Word does not automatically detect the language correctly.*

To change the language for spell check

With your document open in Microsoft Word ™ select the text you wish to spell check or press CTRL+a on the keyboard to select the whole document.
 

Method 1:

1. Click on the language displayed in the bottom left of the Word page
2. In the pop up box select the language you want 
3. Deselect the checkbox that says “Detect language automatically” or it may not set the language you want to spell check in.

Method 2:

1. Click on Review tab at the top of the Word window
2. Click the language button
3. Click “Set Proofing Language“
4. In the language box scroll down and then select the language you want.
5. Deselect the checkbox that says “Detect language automatically” or it may not set the language you want to spell check in.