Comment 26 for bug 1901829

Unfortunately running "find ~/.thunderbird -name langpack*@thunderbird.mozilla.org.xpi -exec rm {} \;" didn't fix it for me. From before running that command, I had just the en-GB language pack:

~$ find ~/.thunderbird -name langpack*@thunderbird.mozilla.org.xpi
/home/<email address hidden>

and had the following thunderbird packages installed:

# dpkg -l | grep thunderbird
ii thunderbird 1:78.3.2+build1-0ubuntu1 amd64 Email, RSS and newsgroup client with integrated spam filter
ii thunderbird-gnome-support 1:78.3.2+build1-0ubuntu1 amd64 Email, RSS and newsgroup client - GNOME support
ii thunderbird-locale-en 1:78.3.2+build1-0ubuntu1 amd64 English language pack for Thunderbird
ii thunderbird-locale-en-gb 1:78.3.2+build1-0ubuntu1 all Transitional English language pack for Thunderbird
ii thunderbird-locale-en-us 1:78.3.2+build1-0ubuntu1 all Transitional English language pack for Thunderbird

As with others, running thunderbird in safe mode works for me.