I recently tried to add internationalisation to my nodes.
Beside the default "en-US" files I added corresponding "de" files.
This works fine if I set my browser language to "de".
But if I set it to "de-DE", it will not fall back to "de" but to "en-US".
It would be nice, if "de-DE" would fall back to "de" first (following the fallback principles of the i18next framework).