Kayak may be able to help you.  ”After a fruitless search online and in Keynote Help (and just when I was on the verge of upgrading MS Office) I did learn how to spell check in foreign languages in Keynote. This works through the following Keynote menu selections:

Edit/Spelling/Spelling then click the tab at the bottom of the window to select your spell check language.

Thanks to Sara at Apple Tech Support!”