I'm wondering if each one is a different version.

Dictionaries are here: 'Menu icon' > 'Add-ons' select the 'Dictionaries' icon - usually the one at the bottom. What have got listed ? Check to see if there are different versions. This is where you remove / disable / enable etc.

No. They are not showing in the Dictionaries section of my Add-ons.

In that section I have the United States English Spellchecker and four non English Dictionaries that also show up in the spell checker. As they should. The 20 other non-US English spellchecker that show up in there have names such as India English, Zimbabwe English, Australia English, etc. They seem to come out of nowhere really (one thing that is clearly impossible).

[Running TB 52.4.0 (64 bits) on Archlinux]

I would guess that they come from you repository. Most Linux Repos repackage Thunderbird and adding a load of dictionaries sounds like something that a repo maintainer would do. Normal dictionaries have a remove and disable button.

Dictionaries listed for download after a search however do not they have an install button.

@Matt, thanks. That could be a pointer in the right direction, although adding even one dictionary beyond the default US-English one, sounds like an Arch repo manager would NEVER do. But then I'm only supposing. I don't know that individual or what he/she/it had the previous night.

Can you suggest a path to start acting toward getting rid of that ? Or is it just getting in touch with the repo team, so they re-package TB ? Or me doing it (in decreasing order of preference).

(This thing plagues me, and I am certain that I am not the only one.)

Cheers, -ced

@Matt, The issue disappeared with Mozilla Firefox v57. Which goes to show it was a mozilla caused issue, not an Arch issue at all.