All default language files are located in: mods/com.phenixidentity-auth-http~<version>/web/res/lang/xx. These are not to be changed since they get overwritten during an update of the server.
The recommended way to change/override all language keys is by adding them to: overlay/auth-http/lang/xx/overlaystrings.xml
All changes in texts / translations will require a restart of the service.
How to use
Open the overlaystrings.xml located in the XX folder within lang with a text editor and add the tag (copied from the default strings.xml). Change the text.
Adding a language
In order to have the custom translations to work, the corresponding language has to exist in the auth-module.
The language folder and files has to be created both in the module and in the overlay if a new language is added to the server