Our WordPress newsletter plugin is available in multiple languages. Check them out.
Most of language files are included in the package so during the AcyMailing installation process, the translations are automatically installed so you don't have to do anything on your end.
In case that a language isn't included, you simply have to go on the AcyMailing Configuration page, tab "Language" and create your own language. AcyMailing will propose you to load the latest version of this language directly from our website. Then you simply have to save the language to have it on your website. Here are the current translations available for AcyMailing, fully or partially: