Using Version 0.62.51 Chromium: 73.0.3683.103 (Official Build) (64-bit)
The US English is the default spell check dictionary, but by default the slider is set to off https://i.imgur.com/OY0Cnn8.png
I had to add the Canadian dictionary to get ANY spell checking to work. But, of course, Canadian English is not the same as American English, and as shown in the photo, US English is still greyed out and disabled.