Somewhat embarrassingly, I mixed up Thunderbird and Firefox. The method should work equally for both though, except that the firefox profiles are stored in ~/.mozilla/firefox
, not ~/.thunderbird
.
As of writing, most answers don't work straight forward or at all anymore. The closest is the recommendation to add content to persdict.dat
, but the answer of Dolanor doesn't work straight forward with modern versions of spell checkers, because the dictionary files typically don't contain all variants of the words -- but rather rules how to form them from a dictionary of base forms.
What I did instead was to use the command
unmunch /usr/share/hunspell/en_US.{dic,aff}
to generate a list of all variants and append that to $HOME/.thunderbird/<PROFILEFOLDER>/persdict.dat
. This should work for any language; In my case I am using a German dictionary in thunderbird, with en_US
added to the persdict.dat
file.
Limitations
While this works in principle, there will remain cases that are not handled well due to rules that go beyond the forming of the words.
With a German main dictionary and an English generated persdict.dat
in particular, the spell checker will complain about constructs like hyphenated English words.
As pointed out by jbrock's comment, this setting also doesn't account for the possibility of English words being capitalized (e.g. title case style). They provided a solution in the comment.