Translate plugin and send us translation files. Notice that files must be in standard WordPress language format.
How to translate plugin
If you are looking for the best method to translate a WordPress plugin, you can use Poedit. There are other ways to realize translate function for WordPress, but this is the most popular: a cross-platform get text catalogues (.po files), editor.
.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
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 the 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
If you do a full or a decent partial translation, submit it to the plugin author, so it 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.