https://github.com/jenstornell/kirby-panel-flags
In a multi language installation of the panel, the language code shows the current language.
Because there is no visual element (only letters) it can be easy to accidentally save the content in the wrong language.
This plugin adds flags as a complement to the language code.

Blueprint
To make it work as expected, add the following code to your blueprint:
fields:
flags:
type: flags
Options
This option can be set in your /site/config/config.php
file:
c::set('plugin.flags.filenames', array(
'en' => 'gb'
));
More info on Github.
2 Likes
While flags seem to be all over the place, I personally don’t like them and I don’t think their use for languages is very appropriate, see also this article or this.
3 Likes
Thank you for that plugin. While this might not fit everyones taste, I can see some of my clients appreciating it a lot. Especially those who accidentally overwrote a language version.
It’s amazing how there’s a discussion about flags in the panel and suddenly Jens “plugin-machine” Törnell releases a plugin. 
2 Likes
Thanks for giving us the option Jens 
2 Likes
I’ve stopped develop this plugin and will not continue with it, so it’s deprecated. Anyone can take it over. I’ve moved it here: