[luatex] loading new language patterns

[Luis Rivera]

I'm trying to understand how to load a new set of language patterns in
plain luatex. This far, I collect I have to do

%%%
\directlua{
grc = lang.new()
pattfile = io.open(kpse.find_file('grchyph.tex'), 'r')
lang.patterns(grc, pattfile:read('*all'))
pattfile:close()
}

\def\greek{\language\grc}

\greek χαῖρε
\bye
%%%

But then I don't know how to access the patterns with a language declaration.

I'm sorry, but I fear the documentation is far too terse on this topic
for a non-programmer. Any hints are welcome.

Thanks in advance,

Luis Rivera