Yes, it is persistent, so absolut you win the "Fix of the Day" award today.
So, in the browser, the language must be set to "English", and not "English (US)".
There is a consequence to changing the setting --- Chromium has a warning that this setting will disable spell checking. I suppose in Great Britain it will be the opposite -- spell checking will
only work with "English" in the browser. But Australians and New Zealanders will have the same issue.