Today you cannot set the English variations in your personal Language settings, you can set English variations in formats, but in Language, English is only available as "English", it is actually set as English US. This has an impact on setting up Knowledge Articles.

The best way to set up the search on the form is to present search results according to the User Default Language, this way they are presented with Knowledge Articles in their preferred language. If you write an article in any English variance other than English-US, the article will not appear in the auto search as the only Language setting for a user is English, this "English setting" is actually English US, so a English- UK/Canada, Australia, New Zealand etc article will not show for a user that has set English as their language automatically. The only way around this is to set the Form control to display as the English UK language, but that means French users do not automatically get their searches, the user has to change the search language manually (if you set this in the form control) to see the result.

If MS can add the English variations to the Language personal setting (like it is in Formats) this will allow the KB to work properly.