Dear Maintainer,

Dialog buttons "Save" and "Cancel" are not translated in all parts of
the UI.  For example, with French (or German) local, they are not
translated in the dialogs form the Compose window:

* Open the compose window (Ctrl+N)
* Type anything in the message body
* Close the window (Ctrl+W)

A dialog box opens asking to whether to save as draft, with the buttons
"Discard changes", "Cancel" and "Save".

The expectation would be that all three buttons are localized.
What actually happens (in French and German locales at least) is that
only the first one is localized, the other two stay in English.

Interestingly enough, this does not happen with the dialog asking
whether to leave offline mode if trying to fetch mails (if you go
offline, then try to fetch mails: that dialog has "Cancel" translated,
although it seems to use the same code internally --
Services.prompt.confirmEx()).

This does *NOT* affect localized binary tarballs downloaded from
upstream.  If I download it from upstream [1] it works fine and both
instances are translated correctly.  Tested upstream's 78, 84b1 and
85b1.

This used to work in Debian's Thunderbird 52 (1:52.8.0-1~deb8u1), but
doesn't since at least 68 (1:68.12.0-1~deb10u1).

Regards,
Colomban

[1] https://download-installer.cdn.mozilla.net/pub/thunderbird/releases/78.5.0/linux-x86_64/fr/thunderbird-78.5.0.tar.bz2