For discussions around programming languages, within GNU, but not specific to a particular GNU package, there is now a mailing list <language-expe...@gnu.org>.
The subscription page is here: https://lists.gnu.org/mailman/listinfo/language-experts You are invited to join if you have extensive experience in this area. Topics will range from programming language design issues to implementation techniques. Possible topics include specific language features, diagnostics, multi-threading / parallel execution, programming styles, just-in-time compilation, and security. Bruno