Get a list of unknown words

I’d like to be able to bring up a consolidated list of unknown words, without doing a full-blown spell-check.

Use Case: To build up lists of place names and character names used. As these are often made-up words, or obscure words in foreign languages, they won’t be in the standard dictionary. Getting a sorted, unique list lets me enter placeholders into the Characters and Places sections, which I can then fill out using the Search function.