I should have elaborated on the testing I did: in a fully up-to-date focal VM with French as the default language/locale, I enabled focal-proposed and installed the thunderbird update (1:78.7.1+build1-0ubuntu0.20.04.1), and I verified that the UI is fully localized in French, including menus, preferences, etc…
I should have elaborated on the testing I did: in a fully up-to-date focal VM with French as the default language/locale, I enabled focal-proposed and installed the thunderbird update (1:78.7. 1+build1- 0ubuntu0. 20.04.1) , and I verified that the UI is fully localized in French, including menus, preferences, etc…