> I was solving the same problem and only solution I've found was to
> parse `language.dat` file, see (some example is at the bottom of the
> file):
> https://github.com/michal-h21/luavlna/blob/master/langno.lua

I'm not sure this is what you are looking for, but in babel 3.9 
\bbl@languages stores a snapshot of the loaded languages in the
form \bbl@elt{<language-name>}{<number>} {<patterns-file>}