Feature #16356: Upgrade to Tor Browser 9.0 (based on Firefox 68)
Spellchecking only available for English in Tor Browser 9
Nothing in Tor's Trac about this.
Note that the Thunderbird maintainer in Debian wrote:
One more important change is the impossibility to use system wide
installed dictionaries. At least I haven't found a way to still use
them. If this can't get changed all the recommends on the dictionary
packages will get useless. If someone can contribute something here to
solve this I'm happy to take this help!
System-wide hunspell dictionaries work in Firefox 68 on my sid system. The firefox (61.0-2) changelog entry reads:
* debian/browser.links.in, debian/rules, debian/vendor.js: Use the spellchecker.dictionary_path pref to set the hunspell directory.
Doing so via about:config in a running Tails 4.0~rc1 fixes the problem.