The String Table Editor can be launched from Window→Localization Editor→String Table Editor.
Managing Languages with the String Table Editor, you can
Creating A New Language
The Add New Language drop down displays all Specific and Neutral cultures. For example, To select es-ES, select Specific Cultures→es-ES - español (España) - Spanish (Spain).
Deleting A Language
To delete a language, first select the language in the Localized Strings drop down. Then click the delete button.
Creating A Custom Language
To create a custom language, select Custom in the Add New Language drop down.
Enter a unique name and click Add Language