In the essay "A Secret Vice" he describes this pastime as lonely and embarrassing. Although the word nerd had not yet entered the English language in 1931, he is clearly describing something all nerds experience when he explains the isolation brought on by the pursuit of a hobby not recognized by the popular or the powerful. He writes:
"Most of the addicts [people addicted to inventing languages] reach their maximum of linguistic playfulness, and their interest is swamped by greater ones, they take to poetry or prose or painting, or else it is overwhelmed by mere pastimes (cricket, meccano, or suchlike footle) or crushed by cares and tasks. A few go on, but they become shy, ashamed of spending the precious commodity of time for their private pleasure, and higher developments are locked in secret places. The obviously unremunerative character of the hobby is against it--it can earn no prizes, win no competitions (as yet)--make no birthday presents for aunts (as a rule)--earn no scholarship, fellowship, or worship. It is also--like poetry--contrary to conscience, and duty; its pursuit is snatched from hours due to self-advancement, or to bread, or to employers."
We can hear in this passage Tolkien's own frustration with duties that prevented him from pursuing his "secret vice" full time and sharing it publicly. He was sure that there were other people out there like him, but before the internet he had no way of meeting up with them. So he continued to toil on Quenya and Sindarin in private. But finally his hobby is having a renaissance. As Philip Seargeant points out in "Why J. R. R. Tolkien's Tradition of Creating Fantasy Languages Has Prevailed" conlangs are now popular, even cool. J. R. R. Tolkien was just ahead of his time, as his shy manifesto, "A Secret Vice" suggests. So fly your word nerd flag high and proud.