The fix for this issue is now available in the latest update of InDesign – that is, InDesign 15.0.3.
Please update your InDesign application to get the fix.
Adobe InDesign team
An error occurred while saving the commentRuth Prickett commented
It's not working in English either. It's driving me mad. My preferences say "English UK" and the spell check still says "English USA" and it acts as if there are no words that need checking. Sort this out urgently!