We have a similar problem where we would want the Custom Dictionary to be created in the Database instead of the Isolated Storage. I searched Telerik forums and found this link
containing an attached file RadSpellCheckerUsingDataBase.zip
containing a Silverlight project.
I unzipped and run the Silverlight project, but before clicking on the "Check" button I cleared the Isolated Storage cache by right clicking the mouse then selecting Silverlight > Application Storage > Delete All. Then I proceeded the click on the "check" button which resulted in the following error. "Initialization Failed - IsolatedStorageException was unhandled by user code" It seems that the Isolated Storage Cache is still being used internally and if you look at the database there are no custom words added from the Custom Dictionary. Is this a bug in the SpellChecker implementation or is there another way to do this.
Hoping for an answer.