The translation system is split up to three parts, each with it's own area of work.

Under the "po" directory, there are three directories, "help",	"js", and "php".

"php" is the main translations of all php files.
"js" are all translations that are using by javascript files
"help" is separate from "php" as they are used by po4a instead of the normal translations routines, thus creating static translated files.

To translate, there are numerous applications available to help with the translation work, for example: poedit, gtranslator, lokalize etc...