As a translator you can expect that the project has been setup appropriately for you and the languages and locales have been defined. You simply have to decide what to translate.
The main project screen
Open the project. The developer of the program has told you where to find the project root. There must be a file called "i18nedit.properties" in it. Double click that file. A new window will appear containing three parts:
On the left, a tree shows the directory structure within the project and all properties files - or, to be more precise - all ResourceBundles. Perhaps you will have to open one or more directories before you see actual files.
When you click on a file name, the list in the middle will be filled with the labels of the localizable items. This list contains everything that is localizable in that specific ResourceBundle.
Clicking on one of the ressource names brings content into the fields on the right side. You see the content of the resource item for each defined locale. If you haven't been told, you'll also be able to see the actual locale names in the "Localization" field.
As long as you do not perform any further setup, you can now access all property bundles, all properties within them, and all locales which are defined for the project. You can edit each and all of them and as soon as you select another properties bundle, all your changes are saved in the project on disk.
If the project has a lot of defined translations, the list on the right can become quite long. In this case, you can open the "Project → Select shown locales" dialog, which allows you to define the locales you want to see. All other locale representations are hidden after this setting has been made.
Select shown locales
Of course, I18NEdit is not only for viewing and generally editing the properties settings. Its real functions for translators hide behind the "Search" menu.
The "Search" menu.
The entries of this menu perform the following operations:
"No search" disables all special search modes and returns to the "Edit everything" mode.
"Search for missing translations" features the most important function of I18NEdit: Performing a directed translation from one language into another and leave everything out which has not changed since the last translation run.
"Search string" allows to look for a certain string in the property values.
"Continue search" continues the search in the current mode and returns the next property which matches the given seach parameters. In "missing translation mode" the next property is found where the translation is missing or outdated, in "string search mode", the next property is shown which contains the given search string in one of the searched locales.
"Check superfluous items" is only used if you are searching for missing translations. If selected, it checks for each property bundle if the target locale has entries which are not in the source locale, if so, it offers to delete them. This helps keeping translations clean if deletions are done in the source locale.
Note that you can perform the "continue search" operation also by pressing the "F2" button.