I've worked through setup of SpellCheck with Aspell so I now have the "ABC" icon on the toolbar in the editor window, and it will spawn the window that does spell checking.
But, no results are reported in the spell check window. The message "Spell checking in progress ... " appears for a half-second, then the window has nothing in it's fields - the text block is empty and "Done" is displayed in the status bar. Intentionally misspelled words are not flagged. (Spell check runs as expected from moodle.org with the same browser - Firefox.)
In Moodle, "English (EN)" is selected as the language; no languages are entered in the LangList field. Running "Aspell dump dicts" confirms that the EN, EN_US, and other variants of English language are available. Aspell runs as expected from the command line.
What next? Thanks to all for your wonderful contributions.