The application is built using Python3, Gtk 3, GLib and other GNOME technologies around it. It's built to run on GNOME & Librem 5 phone.
You can translate Authenticator here: https://l10n.gnome.org/module/authenticator/
You want to work on fixing a bug, adding a new feature, please first join our Matrix Channel and ask if there's anyone working on that already. The Matrix Channel: https://matrix.to/#/#authenticator:matrix.org
We suggest you to use GNOME Builder as the IDE supports Flatpak and you can hack on Authenticator, click on run and voilà, you have got to test your modifications without having to think about installing the dependencies or how to build the application itself.
Thanks and good hacking.