I have 6.8.3; the solutions given here:
... are for version 6.5 or so. The UI items mentioned in the solution are no longer present.
That is, my toolbar doesn't have an ABC button, nor do the Plugins nor Settings -> Backup have any way to disable Auto-Correct. I do see the DSpellchecking plugin but do not see any way to configure it.
I am one of the authors of Working Software's Lookup and Spellswell; bad spellers drive me totally round the bend. (They were originally written by Mike Green and Dave Johnson, I developed new versions.)