I have a Drupal 9 site with 2 languages, English and French; French is the default language. Initially, on /admin/config/regional/language, the visible labels are French and English. When I click on Translate, next to English, French is shown as original. When I visit /admin/config/regional/language/edit/en to change the French translation, I set the language to Anglais instead of English; when I go back to /admin/config/regional/language/edit/en/translate, I see that English is marked as original.
Why does this happen?