Mozilla projects offer to check the spelling in every language installed on your computer. Which is great, except I don't need South African English, nor will I ever use Swiss French. And wading through the 20 items in the menu to switch from Canadian English to Québecois French is annoying.
And there is no easy way to fix this.
The hard way is to go into /usr/share/myspell and remove all the .dic and .aff files you don't want.
$ sudo su - Password for fil@scott: # cd /usr/share/myspell/ # mkdir NOT # mv *.dic *.aff NOT # ln -s NOT/fr_CA.aff # ln -s NOT/fr_CA.dic # ln -s NOT/en_CA.aff # ln -s NOT/en_CA.dicRestart Thunderbird and you will now have 2 spelling options.
Yes, these changes are system-wide. There is currently no other way to do it, apparently.