Does your paragraph style has the correct settings?
- Use not the World composer
- Use correct language direction in Object, Character and Paragraph.
- Take care that no character style overwrites the settings.
Thanks, Willi. That was the problem -- it was set to Arabic. So I switched it back to English, but, hmmmm, it's still red-squigglifying everything. No character styles applied.
You need to select your story fully, I mean highlight your text then apply/change language to English
Take care, that the Paragraph Style is set up correctly.
Turns out all I needed to do was actually run spell check. The red squiggles just stay there after the language is changed, otherwise.