They have an active mailing list: https://www.lua.org/lua-l.html

And they are welcoming towards patches, though they don't copy them all in verbatim: https://www.lua.org/faq.html#1.9

> 1.9 – Do you accept patches?

> We encourage discussions based on tested code solutions for problems and enhancements, but we never incorporate third-party code verbatim. We always try to understand the issue and the proposed solution and then, if we choose to address the issue, we provide our own code. All code in Lua is written by us. See also the previous question [On the lack of a public, official VCS].

Few large projects accept all outside contribution. And Lua would not be as versatile, as portable, or as small as it is if it did.