SendPress in Your Language
SendPress provides you a very simple method for translating the plugin into your own language by letting you create your own translation files and then placing them in an upgrade-safe directory. This short guide will show you how to use your own translations.
The first thing you need to do is create a new folder called sendpress inside of wp-content/languages/. If languages/ doesn’t exist, create it as well.
Once you have created the /wp-content/languages/sendpress/, place your custom .mo file in that folder. The .mo file must be named as follows:
For example, if your language is German, then the file will be named:
Note: Your WordPress installation must be translated as well to translate SendPress.
Creating Translation Files
Translation files must be created for the language you want to use the plugin in. By default SendPress in 15+ languages and if you would like to contribute you can here https://www.transifex.com/projects/p/sendpress/
There is a very popular and easy to use program called POEdit that provides a simple tool for creating translation files.
Note: language files placed inside of /wp-content/languages/sendpress/ take precedence over languages included as part of the core plugin, which means that if you place a copy of one of the language files that SendPress ships with, your custom version will be used instead.