Thunderbird and Firefox have both installed (or shipped with, I don’t know) dozens of languages and dictionaries when I intend to only use the “en-US” locale (with an European format), and do so on all my other devices. Perhaps this happens because the programs retrieve both from the operating system - how to verify what I have installed?
nothing else installed (but that’s just because I want default en on my test system)
dnf info langpacks-core-en
says: This package provides English core langpacks packages.
Re Thunderbird, I checked and I have the same 50+ dictionaries installed. No clue why that is a default… But remember, a langpack has usually nothing to do with a spell-checker (dictionary). Let’s discuss this separately (see link to the other post you provided).