/r/programminglanguages (17.5k subscribers) is a good start. They recently launched a directory of projects (50+) the group is working on: https://www.proglangdesign.net which also links to their IRC and discord servers.

Also there's https://futureofcoding.org which has a growing community of language and tool designers focused on live-coding languages. There's a good number of projects being developed by members there.