If you want to localize a plugin or theme or even just change some wording around, or if you are starting from scratch the easiest thing to do is install the Codestyle Localization plugin.
If starting from scratch, just make sure your plugin or theme loads the file using
[prettify class=”php”] <?php load_plugin_textdomain( $domain, $abs_rel_path, $plugin_rel_path ) ?> [/prettify]
Once that line of code is in the plugin or theme go to Tools->Localization and you should see your plugin or theme listed.
Find your plugin or theme and click on the Add New Language buttton.
Click Rescan. Have it scan the files.
Click on generate mo-file.
Then you’re all done.