Hi @Steve Armitage ,
Thanks for posting in the Q&A.
The policy of DefinePreferredLanguages: If you enable this policy, websites will appear in the first language in the list that they support unless other site-specific logic is used to determine the display language. The language variants defined in this policy override the languages configured as part of the SpellcheckLanguage policy.
1.We could use group policy to change from English US to English UK:
Install administrative templates, add rules and settings for Microsoft Edge, GP unique name: DefinePreferredLanguages
GP name: Define an ordered list of preferred languages that websites should display in if the site supports the language
About configuring Microsoft Edge policy settings on Windows:
2.We could also use the reg key to change it:
Under HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Edge, create a new string value named DefinePreferredLanguages
Set the value to be en-UK
Please refer to this link:
Note: Non-Microsoft link, just for the reference.
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