https://www.askvg.com/tip-enable-automatic-translations-feature-in-mozilla-firefox/#how_to_disable_translations_feature_in_mozilla_firefox

How to Disable Translations Feature in Mozilla Firefox If you decide to disable or remove the new translations feature, simply set the above mentioned preferences/flags browser.translations.enable and browser.translations.autoTranslate to False and restart Firefox. It’ll deactivate and disable the built-in translations feature in your web browser.