I use Google Docs in several classes. One problem that comes up a lot is the spell-checker. If my students’ Drive language isn’t English, their English spell-check won’t work. Here’s how to fix it:

With your document open in Google Docs,

Highlight all your text.

Go to the File > Language menu, and

Select English (United States).

Now you should be able to see any incorrectly-spelled English words (and, of course, correct them!)