https://github.com/jcbvm/i18n-editor can be used to edit the translations files.
To import the OpenPnP files:
- Download and run the tool.
- Drag the folder openpnp/src/main/resources/org/openpnp into the tool's main window.
- Click keys to edit their text.
- Add a new language by selecting Edit -> Add Locale. See https://www.oracle.com/technetwork/java/javase/java8locales-2095355.html for a list of language codes.
Note: There is an issue where a parent of a nested key is not editable in the tool
OpenPnP will detect your language automatically and use the correct language file. If you want to change the language you can select "View->Language" from the top menu.