Comprehensive list of the plural forms required for poEdit when translating different languages.
#localization
poEdit Plural Forms
The strings required to configure poEdit to handle plurals in all sorts of languages
Codestyling Localization
Powerful-sounding plugin to help with the translation process of plugins. It plugs into wp-admin and then allows you to load up what needs translating from another plugin.
Weblog Tools Collection » Blog Archive » Localizing a WordPress Plugin Using poEdit
Weblog Tools Collection » Blog Archive » Localizing a WordPress Plugin Using poEdit
Good tutorial on localizing the language used in plugins and themes via Gettext.