If the language that is passed in through the options is just a
string, like "en-US" or "pt-BR", Select2 will now try to load the
base language along with the requested language and "en". So
requesting "pt-BR" will try to load "pt-BR", "pt", and "en".
This also catches errors and triggers a warning about not being
able to load the file. This should be a more user friendly error,
and it fixes the problem where Select2 would completely fail to
initialize if a language could not be found.
This closes https://github.com/select2/select2/issues/2934.