Messages can be sent to any segmentation of Customers, and these Customers can have different Languages.
To cater for this, rather than just sending everyone an English version of the Message you can define Language Templates for different Languages.
Within the Compose page on a Message click on the New Language button:
Select the Language this template is for and enter the Subject, Preview Text and Body content in the language of the template:
When this Message is sent, we will check the recipients language, and if a Language Template exists for that language, we will send that Template to the Recipient rather than the English template.