Try this:
- After selecting File->Options window
- Click on the Corrections tab on the top row of the options window
- Then select the Spelling item in the left column list
- In the window, right pane, there should now be a dictionary field. Beside that is a Download… button which provides a list of dictionaries that can be downloaded.
- Select your dictionary, and proceed to download.
-Then back on the Corrections pane, beside the Dictionary field is a Select… button. This allows you to pick from the list of available (downloaded) dictionaries.
