I have had this issue for SO LONG and it has been bothering me so much. I have tried every suggestion I came across, but nothing helped. I think I just figured it out, though! The steps I followed are below (I tried to include screenshots, but am unable to add them here for some reason):
- Hover over one of the underlined words and click on it.
- A small "Spelling" pop-up will appear. On the bottom right of that pop-up, click on the "Editor" (it has a little pen icon next to it) button.
- An "Editor" sidebar should open on the right. At the very bottom of it, there should be a "Settings" section, click on the "Customize your Editor" option.
- "Microsoft Editor Settings" will pop up. Choose "Manage spellcheck languages" > "Add another language" > choose the English relevant to you > "Add" > "Done" >"OK"
I REALLY hope this helps!