Chrome Version: 64.0.3282.169
Chrome OS Version: 10176.73.0
Chrome OS Platform: Pixelbook
Network info: WPA2-PSK, Netgear R7000

Steps To Reproduce:
(0) Somehow add Chinese as a language (not sure how kids did it)
(1) Click lower right profile icon
(2) Click gear
(3) Search for "language" or ”語言“

Expected Result:

The ability to delete languages and select "Chrome OS is displayed in this language" for the language you want.

Actual Result:

You cannot delete languages and you cannot select which language you want for Chrome OS. The selection is disabled and this is massively frustrating because there is no documentation that states how a user can accomplish this goal.

How frequently does this problem reproduce? 

Unsure. The account got in this weird state where 英文 and 中文 were the two languages available. Chrome OS was showing 中文 and since my daughter is not fluent, I wanted to switch back to 英文，which I believe to be the default locale.

What is the impact to the user, and is there a workaround? If so, what is
it? 

Frustration is the impact. The workaround is to add 英文（美國）and then select that as the language to display in Chrome OS.