The vanilla Thunderbird version from https://www.thunderbird.net/ does not install tons of dictionaries by default. You did install a flatpak version presumably provided by your distribution. So you should ask in a support forum for your distribution.

Tools/Add-ons & Themes, Dictionaries section, unwanted dictionaries can be removed.

Yes, it is flatpak install. Additionally I have only 2 dictionaries that offers several versions of English Canadian, US, British, . . . as you can see the attached pic.

Depending on the Linux distro and the packages it is possible the dictionaries are installed as individuals or as a bundle package separate from the Thunderbird package in your package manager.

Only a few languages of the official Thunderbird (and Firefox) builds even comes with a dictionary due to licensing reasons.

I realized the terminology: Laguage packs installed only 2: English(en-GB) Hungarian

Dictionaries: too many, I never installed any of them English(US, Zimbabwe, Trinidad & Tobago, South Africa, Namibia, Jamaica, New Zealand. . . .) I think no reason to install this kind of dictionaries to me. I guess if I remove the English language pack the dictionaries will remain here. Am I right?

Language Packs are used as a way to change the UI language with one install, they are not used by the spell checker.

The Spell checker uses Dictionaries.

On https://addons.thunderbird.net/en-us/thunderbird/language-tools/ there are only five English as in English (Australian), English (British), English (Canadian), English (New Zealand), English (US)