I think this is a good step but what we really need is the ability to have multiple dictionaries active at the same time, not just one.  We thought about working around the need for multiple active dictionaries by combining all of our custom dictionaries with the Telerik base English dictionary from the website into a single 380,000+ word dictionary and using that but there is no way for us, at runtime, to convert our Word custom dictionaries to .tdf format so that we can concatenate all of these dictionary files together.  Our custom dictionaries are unique to each client and are downloaded from our server so we can't use the Dictionary Configurator web application and the conversion methods called by the Dictionary Configurator are not available in your WPF product.  This would solve our problem if we could download the Telerik base English dictionary as a word list so we could concatenate it with our custom dictionaries to create a single spell checking dictionary.