I’ve red on another site, that on Linux Thunderbird uses the hunspell package for spellchecking. so basically the same as stated above.
Unfortunately for me restarting Thunderbird or Solus after the install of hunspell does not change anything for the available spellchecking dictionary, which is still only the one for english. I know, that using a dictionary as addon would work, but from the posts above it seems, that at least for some the hunspell variant also works?
