@yubiuser I think you're confusing something here. This seems to be designed for the React web interface
which was originally planned to become v6.0. I think this is outdated. I recall having seen a comment somewhere that due to the lack of core developers being able to deliver a complete React framework within acceptable timescales this project seems to be postponed to some post-v6.0 (or maybe it even gets abandoned?). Pinging @DL6ER for confirmation if my conclusions are right or bullshit.
This may be what you are looking for with the current web interface: https://adminlte.io/themes/dev/AdminLTE/pages/examples/language-menu.html
They always welcome pull requests (I will do one myself, soon, first I have to get an idea and then learn PHP, however 
)