Looks like this was added already via bug 1877203! I'm going to improve the documentation around this area. It is easy to miss what APIs are implemented and not implemented. I'll update this bug with better documentation shortly.
Bug 1881814 Comment 1 Edit History
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Looks like this was added already via bug 1877203! I'm going to improve the documentation around this area. It is easy to miss what APIs are implemented and not implemented. I'll update this bug with better documentation shortly. Edit: Realize I just saw `updateLanguageSetting` which is the path for the page settings, not global settings. So, this bug is still valid, but more just adding the action, and less connecting the API.