Plugin Manager is called Plugin Admin and you check the box for DSpellCheck and click Install. You get US English.
Doesn't know some words, like "arbitered" or "minorly", so it's not like it's Merriam. But if you're confident and just want to catch the occasional mistype (as opposed to misspell), it's OK.
Looks like you can change the language later, bunch of options that make no sense to language experts. I know 3 well enough to call false squiggles. In general, the world is waiting for the awesome spell checker, but since billion corporations can't, I guess we have to wait until devs call for the help of dictionary publishers.
Wanted to share an updated answer and what to expect/rely on.