This was one of my example questions but I now am actually interested in the answer. I am an amateur conlanger; I have one pretty complete language and a couple in the process. But I can't construct a sentence in any of my languages without referencing the lexicon and grammar. How common is it for the creator of a conlang to be fluent in that conlang? (especially for languages that are not meant to be spoken like all of Tolkien's, where there is not a very significant fluent community).