I agree with Gord.... the only need to implement a Spell Check is for "non-standard" wordings that exist in a fantasy / Sci-fi setting....
Implementation of this is a low priority in comparison to other elements on the work front for LWD.....
Just as RW is not intended to be a VTT, its not intended to replace your preferred word processor either.
You might find this free ware does what you need. I have tested it with in RW and it works fine....
Note, the default for the word list is the left shift key ,I being left handed find this abit annoying, so I changed it to the arrow down when wanting to view the list to choose from. As Gord has suggested, it also allows you to define your own words as well.
Tiny Spell>
http://tinyspell.numerit.com/#download
DLG