Norwegian Lingua Franca
Vivaldi replaces my url I use to access gmail with another url, resulting in a Norwegian interface. The url it imposes is https://mail.google.com/mail/u/0/#inbox becomes https://www.google.com/intl/no/mail/help/about.html#inbox in Chrome it becomes https://www.google.com/intl/en-GB/mail/help/about.html#inbox Checkout the different urls as listed here https://techjourney.net/gmail-access-methods-and-login-link-urls/ and ensure that Vivaldi does not mess them up Regards, the Viking
Never face this problem personally, I asked to other testers from different nations and they never had the problem as well.
Please try Right Mouse button on any text field and check the language settings you have.