There are group policy settings now available to control this feature:-
In "Google" -> "Google Chrome" there are now 2 entries-
"Enable or disable spell checking web service"
"Setting the policy to Enabled puts a Google web service in use to help resolve spelling errors. This policy only controls the use of the online service. Setting the policy to Disabled means this service is never used.
Leaving the policy unset lets users choose whether to use the spellcheck service.
The spell check can always use a downloaded dictionary locally unless the feature is disabled by SpellcheckEnabled in which case this policy will have no effect."
and
"Enable Spellcheck"
"Setting the policy to Enabled turns spellcheck on, and users can't turn it off. On Microsoft® Windows®, Google Chrome OS and Linux®, spellcheck languages can be switched on or off individually, so users can still turn spellcheck off by switching off every spellcheck language. To avoid that, use the SpellcheckLanguage to force-enable specific spellcheck languages.
Setting the policy to Disabled turns off spellcheck from all sources, and users can't turn it on. The SpellCheckServiceEnabled, SpellcheckLanguage and SpellcheckLanguageBlocklist policies have no effect when this policy is set to False.
Leaving the policy unset lets users turn spellcheck on or off in the language settings."
There are other settings related to languages as well but as it says, they are enabled/disabled by these settings.
I hope you find this useful.
George S
PS: Now to find the same settings for Microsoft Edge.