You may also consider asking r/linguisitics.
Hi! You'll find quite a bit of discussion on Richard/Dick and other similar nicknames in these posts
How did "Dick" go from being one of the most popular nicknames in America for a boy named Richard to a phallic nickname that has caused many of those men to shun being called "Dick"? - follow the links - there's much more on these names downstream
How did names like Robert and John turn into nicknames like Bob and Jack?
All of the posts have been archived, so if you have follow-up questions, just ask them here and tag the relevant usernames to notify them