Comment 5 for bug 1478405

More news.

Plasma 5 seems to use hunspell library for spellcheck, but does not look for hunspell dictionaries...
Removing hunspell dictionaries and installing myspell dictionaries improves the situation

The regional settings -> spell check configuration in plasma 5 is still a mess, because it lists hyphenation dictionaries ad gets insane or repeated entries.

However now I have a working 'American English (United States) [US]' entry at last.

This goes side to side with a non working

American English (United States) which picks "en" instead of "en_US" as a language selector for hunspell and fails

and a nonsensical (but working)

American English (United States) [GB] if it is GB, it is not American English United States, is it?