This is not a complicated or important enough problem to justify a team-wide policy. Let it work itself out naturally.
https://git-scm.com/docs/git-check-ignore makes it trivial to debug repo-wide gitignore behavior.
I heard facebook allows any language as long as you have packaged it neatly with all required build chain. (I.e. Even a choice of language works out)
Some lowest common denominator will be reached. (1 :) )
On the other hand: Are we happy with the lowest or do we want to aim higher?
