How to translate a plugin via .po .mo?

Question

I want to translate this plugin. This plugin already has translations to some languages, and it has .pot file for adding new languages (as far as I understood from description). Although I never had an experience to work with .po .mo
So I wonder what are the main points. How to create .po .mo files and how to define that the plugin will talk a certain language, I tried to define for examble russian language, but did not find where to do this [I tried to insert define ('WPLANG', 'ru_RU'); in wp-config.php but it does not help].

Answer 1

The Editor

There are others, but this is most used: Poedit, a cross-platform gettext catalogs (.po files) editor.

The Formats

• .mo stands for Machine Object
  -- compiled export of the .po file which is used by WordPress
• .po stands for Portable Object
  -- editable text file with the translations strings
  -- based on the master .pot file, using Update from POT file PoEdit function
  -- some folks distribute this as a master file, but it should be used only for translations
• .pot stands for Portable Object Template
  -- editable text file used to grab all the translatable strings from WordPress itself and Themes and Plugins, using Update from Sources PoEdit function

The Procedure

• Duplicate the .pot file and rename it to plugin-basename-lang_COUNTRY.po
• Example for the referenced plugin case: subscribe-reloaded-pt_BR.po
  -- pt_BR means Portuguese Brazil, but many languages don't have a country variation...
  -- you'll have to fill in with your own language
• WPLANG in wp-config.php file must be set to your language, e.g., pt_BR
• Every time you save the .po file, PoEdit automatically generates a .mo file, which is the one WordPress uses and basically the only one you need to upload

Observations

• If you do a full or a decent partial translation, submit it to the plugin author so he can include it in the Repository and you get credited for it
• Don't forget to make a backup of your translation, because if you upgrade the plugin your file will be lost
• @user17078 plugin suggestion is quite nice, but I never used it much
• I left the writing of this answer opened for a while and @Pippin answered in the interim, but am publishing anyway... :)

Answer 2

I suggest also http://poeditor.com/. It is a web-based translation tool that works great with .po, .mo, .pot and other types of files.

Answer 3

try this plugin: http://wordpress.org/extend/plugins/codestyling-localization/ You can translate you plugins and themes using this.

Answer 4

You will want to use POEdit. It's a free application for creating .po/.mo files.

I wrote a pretty in-depth tutorial on the entire topic here. You can skip to Step 3 - Create the Translation File For Text Domain.