There is a GUI editor for the .pong.in (untranslated) files, called PonG-Edit (command line is just "pong-edit". It is fairly simple to use once you understand how .pong(.in) files are structured. It allows you to change and test the PonG file without having to recompile your application, making development easier.
The way translations work is that the file that PonG-Edit generates has some strings marked for translation, this file is normally saved with the extention .pong.in. You should then use xml-i18n-tools on this file to generate a new file called .pong which has the translations merged in. The .pong.in file will in fact also work when loaded with the library, just like the .pong file, you will just not have any of the translations.
PonG-Edit can generate GConf schema files, but without translations, you should really use pong-gconf-schema-export program described below. That program takes a .pong file with the translations merged in by xml-i18n-tools and generates a GConf schema file with all translations done properly.