Here is the fix for not being able to "edit spelling dictionary".
Once you follow the path given to you by the previous poster to the the "Proof" folder then the "lex***file".
When you double click Lex*** file and choose (open with Notepad) keep the checkmark next to "always open this file with this program".
I tried this having over 80 words in my lex file. I cut them all, saved the file with no words in it. Then closed all the windows. I reopened WLMail (I have version 2009 - don't like 2011) and was able to use the edit feature with my default language.
I then pasted the 80 words I cut back into the Lex*** file saved the file and then closed all the windows again. I then opened WLMail and was able to edit with 80 words in the Lex*** file.
I searched for a registry edit but cannot find one. I think some where along the line the Lex****file gets dissasociated from Notepad.
Telling your system to always open the Lex file with Notepad seems to be the fix. I hope that helps anyone who enjoys WLMail. (only email program I like because it synchs with my online folders without having to use IMAP settings in other email clients).