prestaify MailDesigner includes ready-made base templates for: German, English, French, Spanish, Italian, Dutch, Polish and Portuguese.
If your language is not among them, the following happens automatically: The module uses the English template as a starting point for your staging area. You can then translate and customise it as needed in the template editor — branding (colours, logo, footer) will be applied automatically, just like for all other languages.
In short: The module works with any language active in your PrestaShop. You simply start with an English template instead of a pre-translated one.